Added mappings updater

Implemented a mappings updater script that uses the Waifus-Grace/NTE_Assets repo to export all the required mappings.

docs/mapping-updates.md

@@ -0,0 +1,95 @@
+# Reward mapping updates
+
+`tools/update_mappings.py` rebuilds `arcs.json`, `characters.json`, and
+`items.json` directly from the current
+[`Waifus-Grace/NTE_Assets`](https://github.com/Waifus-Grace/NTE_Assets)
+tables. No other exporter or intermediate mapping format is used.
+
+English display names come from `Localization/en/game.json`. The data tables
+provide localization namespace/key references and quality metadata; their
+embedded `LocalizedString` values are deliberately ignored.
+
+The generated files are an authoritative snapshot, not an additive merge.
+When NTE_Assets removes an ID, changes its casing, or updates its metadata, the
+staged mapping reflects that change. This is intentional for a live-service
+game whose asset tables evolve over time.
+
+## Review workflow
+
+### GitHub Actions
+
+Run **Update reward mappings** from the repository's Actions tab. The optional
+`source_ref` input accepts an NTE_Assets branch, tag, or commit and defaults to
+`main`.
+
+The workflow rebuilds the mappings, runs the complete test suite, uploads the
+JSON review report, and opens a pull request from
+`dev/automated-mapping-update`. Running it again updates the same open pull
+request. If the authoritative snapshot has not changed, it reports zero changes
+and does not create a commit or pull request.
+
+The repository setting **Allow GitHub Actions to create and approve pull
+requests** must be enabled for automatic pull-request creation. The workflow
+uses only the repository-scoped `GITHUB_TOKEN` and grants it `contents: write`
+and `pull-requests: write` permissions.
+
+### Local
+
+Stage the latest candidate files without touching the committed mappings:
+
+```powershell
+python tools/update_mappings.py
+```
+
+The required JSON tables are downloaded from the `main` branch by default.
+Pin a tag, branch, or commit for reproducible review:
+
+```powershell
+python tools/update_mappings.py --source-ref e9752e5963103529f0d683fd0aed4752b7dfad78
+```
+
+To use an existing local checkout without network access:
+
+```powershell
+python tools/update_mappings.py --assets-root path\to\NTE_Assets
+```
+
+The default output is `build/mapping-update/` and contains the three candidate
+mapping files plus `mapping-update-report.json`. The report lists additions,
+updates, and deletions by file and records SHA-256 hashes for every source
+table.
+
+After reviewing the report and diff, apply the validated snapshot explicitly:
+
+```powershell
+python tools/update_mappings.py --apply
+python -m pytest -q
+```
+
+For CI, `--check` exits with status 1 whenever the generated snapshot differs
+from the committed reward mappings. It still writes the staged artifacts.
+
+## Source rules
+
+- Every Arc in `DT_ForkItemData` is emitted to `arcs.json`.
+- Every character in `DT_Character` is emitted to `characters.json`.
+- Other pull rewards are selected by `GachaIllustrate` and resolved to the
+  inventory tables for quality and localization keys. Appearance-table IDs
+  provide canonical casing for glider rewards.
+- Names are resolved strictly through `Localization/en/game.json`. A missing or
+  ambiguous key fails the update instead of falling back to a DT value.
+- Character-awakening illustration entries are not independent pull rewards
+  and are excluded.
+- Orange, purple, and blue item qualities map to `S`, `A`, and `B`.
+
+## UID compatibility boundary
+
+This updater reads and writes only the three reward mapping files. It never
+reads or writes the permanent, limited, beginner, or Arc pool mapping files.
+Banner IDs, timestamps, record ordering, format version, and all UID inputs are
+therefore unchanged by mapping synchronization.
+
+Reward IDs and display metadata may change or disappear when the authoritative
+NTE_Assets snapshot changes. Existing exported history files remain unchanged;
+new exports describe rewards using the current asset snapshot. UID stability is
+independent of reward display mappings.