Update task metadata/docs and JLPT tokenizer work

docs/configuration.md

@@ -558,6 +558,8 @@ See `config.example.jsonc` for detailed configuration options.
 | `jlptColors`      | object      | JLPT level underline colors object (`N1`..`N5`)                               |
 | `secondary`       | object      | Override any of the above for secondary subtitles (optional)                  |
 
+JLPT underlining is powered by offline term-meta bank files at runtime. See [`docs/jlpt-vocab-bundle.md`](jlpt-vocab-bundle.md) for required files, source/version refresh steps, and deterministic fallback behavior.
+
 Secondary subtitle defaults: `fontSize: 24`, `fontColor: "#ffffff"`, `backgroundColor: "transparent"`. Any property not set in `secondary` falls back to the CSS defaults.
 
 **See `config.example.jsonc`** for the complete list of subtitle style configuration options.

docs/jlpt-vocab-bundle.md

@@ -0,0 +1,59 @@
+# JLPT Vocabulary Bundle (Offline)
+
+## Bundle location
+
+SubMiner expects the JLPT term-meta bank files to be available locally at:
+
+- `vendor/yomitan-jlpt-vocab`
+
+At runtime, SubMiner also searches these derived locations:
+
+- `vendor/yomitan-jlpt-vocab`
+- `vendor/yomitan-jlpt-vocab/vendor/yomitan-jlpt-vocab`
+- `vendor/yomitan-jlpt-vocab/yomitan-jlpt-vocab`
+
+and user-data/config fallback paths (see `getJlptDictionarySearchPaths` in `src/main.ts`).
+
+## Required files
+
+The expected files are:
+
+- `term_meta_bank_1.json`
+- `term_meta_bank_2.json`
+- `term_meta_bank_3.json`
+- `term_meta_bank_4.json`
+- `term_meta_bank_5.json`
+
+Each bank maps terms to frequency metadata; only entries with a `frequency.displayValue` are considered for JLPT tagging.
+
+## Source and update process
+
+For reproducible updates:
+
+1. Obtain the JLPT term-meta bank archive from the same upstream source that supplies the bundled Yomitan dictionary data.
+2. Extract the five `term_meta_bank_*.json` files.
+3. Place them into `vendor/yomitan-jlpt-vocab/`.
+4. Commit the update with the source URL/version in the task notes.
+
+This repository currently ships the folder path in `electron-builder` `extraResources` as:
+`vendor/yomitan-jlpt-vocab -> yomitan-jlpt-vocab`.
+
+## Deterministic fallback behavior on malformed inputs
+
+`createJlptVocabularyLookupService()` follows these rules:
+
+- If a bank file is missing, parsing fails, or the JSON shape is unsupported, that file is skipped and processing continues.
+- If entries do not expose expected frequency metadata, they are skipped.
+- If no usable bank entries are found, SubMiner initializes a no-op JLPT lookup (`null` for every token).
+- In all fallback cases, subtitle rendering remains unchanged (no underlines are added).
+
+## Bundle size and startup cost
+
+Lookup work is currently a synchronous file read + parse at enable-time and then O(1) in-memory `Map` lookups during subtitle updates.
+
+Practical guidance:
+
+- Keep the JLPT bundle inside `vendor/yomitan-jlpt-vocab` to avoid network lookups.
+- Measure bundle size with:
+  - `du -sh vendor/yomitan-jlpt-vocab`
+- If the JLPT source is updated, re-run `pnpm run build:appimage` / packaging and confirm startup logs do not report missing banks.