fix(build): keep tests/*.mjs out of tsc input; cover *.mjs in lint/format

[RibatTRW]

What

With a plain-node regression script present under tests/, building with

npx tsc --project tsconfig.production.json && node scripts/build-plugin-manifest.js

produces an EMPTY plugin manifest: .dist/plugins.json reports | Total | 0 (0) |, so any downstream "plugin X absent" assertion passes vacuously.

Why / how

• tsconfig.production.json sets allowJs: true, defines no rootDir, and its exclude array lists neither tests/** nor any .mjs pattern.
• A tests/regression-*.mjs file therefore enters the tsc program; the inferred rootDir becomes the repo root; emit lands nested at .js/plugins/plugins/<lang>/<file>.js plus .js/plugins/tests/regression-N.mjs.
• scripts/build-plugin-manifest.js scans ./.js/plugins/<lang>/, finds nothing, and writes [].

Fix (4 files, +6/-4):

1. tsconfig.json and tsconfig.production.json: insert "./tests/**" into exclude, right after the existing "scripts/**" entry (same convention: tooling that plain node runs, tsc ignores).
2. eslint.config.js: extend the project-rules files glob from {ts,tsx,mts,cts,js,cjs} to {ts,tsx,mts,cts,js,cjs,mjs,mjsx}; that config object already registers node globals, which the .mjs scripts need.
3. package.json: add mjs to the format / format:check globs and to lint-staged.

No rootDir change, no emit-layout reshaping, no manifest-script edit.

Tests

Executed locally on 2026-08-25 at base e1dcd06 (RED baseline) and at this branch head (GREEN); tsc 5.9.3, node v26.5.1.

Gate	Base (no fix)	This branch
tsc -p tsconfig.production.json	exit 0 but nested emit: .js/plugins/plugins/{arabic..vietnamese} and .js/plugins/tests/regression-2453.mjs; manifest | Total | 0 (0) | (RED)	exit 0; no .js/plugins/plugins, no .js/tests; manifest | Total | 117 (68) |
Placement equivalence: tests/ moved out of tree, fresh rebuild	n/a	identical | Total | 117 (68) | (tsc input scope no longer depends on test placement)
eslint on tests/**/*.mjs + eslint.config.js	3 false no-undef errors on regression-2453.mjs (console x2, process)	exit 0
prettier --check on package.json, eslint.config.js, tsconfig.production.json, tests/*.mjs	-	all clean (tsconfig.json keeps pre-existing upstream style debt, deliberately untouched)
regression harness run	byte-identical stdout and exit code before vs after (its own PASS/FAIL verdict belongs to #2453/#2468)

Context for the totals (2026-08-25): #2468 (RanobeHub retirement) is OPEN, so 117 (68) is correct against current master; once it merges, the expected total becomes 116 (67). #2466 (Riwyat) is OPEN too; if it lands first, its eslint config object and this glob extension are separate hunks that compose cleanly.

Gates

• Branch diff vs e1dcd06: exactly 4 files changed, +6/-4, nothing else; no lockfile churn; no CI workflow edits.
• .github/workflows/publish-plugins.yml untouched.

Closes: none (repo-level build defect, no upstream issue).

Automated contribution via Hermes Agent.