Disambiguate Fetch Data's TMDB search results by name similarity

- New crates/renamr-core/src/similarity module: a partial port of the
  scoring idea behind FileBot's EpisodeMetrics.java - normalizes titles
  (lowercase, strips a trailing release-year parenthetical, collapses
  punctuation/whitespace) and scores them with a Sorensen-Dice coefficient
  over character bigrams. best_title_match() picks whichever candidate is
  textually closest to the query, provided it clears a minimum threshold;
  ties keep the earlier (i.e. TMDB-ranked) candidate.
- TmdbClient::lookup_episode now uses best_title_match instead of blindly
  taking the first search result, so a more popular but differently-named
  show can no longer beat an exact-but-lower-ranked match to the top - and
  reports NotFound instead of guessing when nothing in the results is a
  plausible match at all.
- 7 new tests (5 in similarity, 2 in tmdb) including the concrete regression
  case this fixes: searching "Chuck" with TMDB returning "Chucky" ranked
  above "Chuck" now correctly picks "Chuck".
- Also fixes a gitignore gap from last delivery: the _to_delete*/ scratch-dir
  pattern used to work around this repo's mounted-folder git-lock quirk had
  only ever been applied directly on the device, never carried back into the
  zip this delivery is built from - so the last delivery's cp -rf silently
  reintroduced the untracked-lock-file risk. Fixed in both places now.

README.md

@@ -7,11 +7,12 @@ fork), built from scratch as its own project: new stack, new architecture, new b
 engine is ported and tested, the faithfully-recreated two-pane UI is wired to real
 native file/folder loading and drag-and-drop, local filename-based season/episode
 detection ("Match") is working, real online metadata lookups against TMDB ("Fetch
-Data") are working, and the actual on-disk rename operation is wired up (same-directory
-rename, skip-on-conflict, with a confirmation step showing the full old-name/new-name
-plan before anything touches disk — there is no undo yet). Full media-metadata
-bindings and the fuzzy similarity/matching engine are not yet ported. See "Porting
-roadmap" below.
+Data") are working — including fuzzy show-name disambiguation, so a search that
+returns several similarly-named shows doesn't just take TMDB's top-ranked hit — and the
+actual on-disk rename operation is wired up (same-directory rename, skip-on-conflict,
+with a confirmation step showing the full old-name/new-name plan before anything
+touches disk — there is no undo yet). Full media-metadata bindings are not yet ported.
+See "Porting roadmap" below.
 
 The naming scheme is fully user-editable from the app (the "Naming Scheme" button next
 to the New Names list) — the default is `{show name} - {season number}x{episode
@@ -81,14 +82,16 @@ rendered output would be empty.
 
 ```
 crates/renamr-core/   Pure Rust core: naming-expression engine (ported), local
-                       filename-based season/episode matching (ported, `matching/`), a
-                       TMDB metadata client (`web/tmdb.rs` — TV search + episode lookup,
-                       tested against a mocked HTTP server via `mockito`), and the
-                       on-disk rename engine (ported for the same-directory case,
-                       `rename/`) — skip-on-conflict, no move/organize-into-folders yet.
-                       Not yet ported: the fuzzy similarity engine, full media metadata
-                       bindings, other web datasource clients (TVDB/AniDB/etc). No Tauri
-                       dependency, so it builds and unit-tests standalone.
+                       filename-based season/episode matching (ported, `matching/`),
+                       text-similarity scoring for disambiguating search results
+                       (`similarity/`, partial `EpisodeMetrics` port), a TMDB metadata
+                       client (`web/tmdb.rs` — TV search + episode lookup, disambiguated
+                       via `similarity/`, tested against a mocked HTTP server via
+                       `mockito`), and the on-disk rename engine (ported for the
+                       same-directory case, `rename/`) — skip-on-conflict, no
+                       move/organize-into-folders yet. Not yet ported: full media
+                       metadata bindings, other web datasource clients (TVDB/AniDB/etc).
+                       No Tauri dependency, so it builds and unit-tests standalone.
 src-tauri/             Tauri app shell: exposes renamr-core as commands to the frontend
                        (naming-scheme rendering, filename matching, TMDB metadata fetch,
                        executing a rename plan, native file/folder dialogs, drag-and-drop
@@ -160,21 +163,25 @@ ported from, for anyone picking this up:
 3. **Matching/similarity engine** — `net.filebot.similarity.*`. Local filename-based
    season/episode detection is done (`crates/renamr-core/src/matching`, ported from the
    pattern-matching half of `SeasonEpisodeMatcher.java`, adapted to Rust's `regex` crate
-   which lacks lookahead/lookbehind — wired to the "Match" button). Now that TMDB is
-   wired up (see item 5 below), `EpisodeMetrics.java` (849 lines, the fuzzy title-matching
-   score cascade) is the next thing this actually blocks on: today "Fetch Data" just
-   takes TMDB's first (TMDB-ranked) search result, which is right most of the time but
-   has no way to catch a wrong pick among several similarly-named shows. `DateMatcher`
-   also still not ported.
+   which lacks lookahead/lookbehind — wired to the "Match" button). Show-name
+   disambiguation is also done (`crates/renamr-core/src/similarity`, a partial port of
+   the *scoring* idea behind `EpisodeMetrics.java`'s fuzzy title-matching cascade —
+   Sorensen-Dice similarity over normalized-title character bigrams): "Fetch Data" now
+   picks whichever TMDB search result is textually closest to the local guess rather
+   than just trusting TMDB's relevance/popularity-ranked first hit, and reports "not
+   found" instead of guessing when nothing in the results is a plausible match at all.
+   `DateMatcher` (numbering/air-date-based identification, the other half of the
+   original `EpisodeMetrics`) is not ported — Renamr doesn't do date-based episode
+   identification.
 4. **Media detection** — `net.filebot.media.MediaDetection` (1356 lines): ties file-name
    parsing + matching together to auto-identify what a file is.
 5. **Web datasource clients** — `net.filebot.web.*` (~40 files): TheMovieDB, TheTVDB,
    AniDB, OMDb, TVmaze, OpenSubtitles, etc. TMDB is done for TV (`crates/renamr-core/src/web/tmdb.rs`,
    `reqwest` + `serde_json`, Bearer-token auth) — search-by-name plus per-season episode
-   lookup, wired to "Fetch Data". Picks the first (TMDB-ranked) search result rather
-   than disambiguating between multiple plausible shows — a real fix needs the
-   `EpisodeMetrics` fuzzy-matching port above. TMDB movie lookup and all other sources
-   (TheTVDB, AniDB, OMDb, TVmaze, OpenSubtitles) are not yet started.
+   lookup, wired to "Fetch Data", disambiguating multi-result searches via the
+   similarity-scoring pass described in item 3 above rather than blindly trusting
+   TMDB's top-ranked hit. TMDB movie lookup and all other sources (TheTVDB, AniDB,
+   OMDb, TVmaze, OpenSubtitles) are not yet started.
 6. **Rename engine + CLI** — `net.filebot.cli.CmdlineOperations` (1235 lines) and
    `ArgumentBean` (415 lines, the full flag surface: `-rename`, `--db`, `--format`,
    `--action`, `--conflict`, `-get-subtitles`, `-script`, etc.). The core same-directory