feat(lang): add Visual Basic 6 / VBA grammar (harumiWeb/tree-sitter-vba)

[Tokarzewski]

What does this PR do?

Adds Visual Basic 6 / VBA as a language (CBM_LANG_VB6) — part two of #721, following the merged short-term disambiguation in #2074. The VB6 .frm/.cls files that #2074 routed to "unsupported" now parse with a real grammar; .bas/.ctl/.dsr/.pag are mapped directly.

Refs #721.

Grammar: harumiWeb/tree-sitter-vba @ 63b2f8d0d65c (v0.13.0, MIT, ABI 15, lexer-only — no external scanner). It parses the module export headers natively (VERSION, Begin … End, BeginProperty … EndProperty, GUID blocks, Attribute lines), so the .frm designer block flagged in #721 as the main technical risk needs no preprocessing step — it becomes ordinary frm_begin_block nodes and the code below parses normally. VB6-specific statements are covered (Declare, Implements, Event/RaiseEvent, WithEvents, Property Get|Let|Set). Rejected alternatives: arrmee-wt/tree-sitter-vba (GPL-3.0 — outside scripts/license-policy.json), joannefan/tree-sitter-vb6 (no licence file, no generated parser, .frm metadata "poorly parsed" per its README), CodeAnt-AI/tree-sitter-vb-dotnet (VB.NET — that is #1073).

Provenance caveat — please decide: upstream gitignores src/parser.c, so the vendored 46 MB parser.c was generated from the pinned grammar.js with tree-sitter-cli 0.26.9 (tree-sitter generate --abi 15, the project's own pnpm generate). Byte-identity with an upstream artefact therefore cannot be claimed; MANIFEST.md records the exact regeneration command (the vba row is marked NOT-IN-REGISTRIES (see note)). The size comes from per-keyword case-insensitive expansion; lean's parser is 102 MB, so it is within precedent.

Extraction (generic paths plus small language hooks):

• Sub/Function/Property Get|Let|Set/conditional_*_declaration/Declare Sub|Function/Event → callables (every kind exposes a name field). Type … End Type → Class with typed Fields (As clause unwrapped, so a Field is Long, not As Long); Enum → Enum with members; module-level Dim/Const → one Variable per declarator; Implements → import.
• Calls: call_statement (callee field — Foo 1, Call Foo(1), obj.Bar x), call_expression (function field — y = Foo(1); VB6 syntax cannot distinguish this from array indexing, unresolved callees just produce no edge), raise_event_statement (event). Dotted obj.Method is kept dotted; With-block .Method yields the bare member name; nested a(1)(2) is unwrapped.
• VB6 reserved words/intrinsic types for cbm_is_keyword; source_file as module parent.

Everything a new grammar needs here (modelled on #1888): enum, lang_specs.c row, language table (the #2074 sniffers now return CBM_LANG_VB6; discover.h docs updated), userconfig.c names (vb6, vba, vb, visualbasic), tests (test_language.c, grammar regression case + label golden, lang_contract CALL case, test_extraction.c), the four repro registries, the seven language-count surfaces 162→163 (README.md, docs/index.html, docs/llms.txt, pkg/npm/README.md, chocolatey nuspec, scripts/package-release.sh, server.json) with tests/test_language_count_contract.sh passing, MANIFEST.md (row, ABI tally recounted from the tree, re-vendor note, custom-extraction-handling entry), THIRD_PARTY.md, scripts/vendored-checksums.txt (sha256 of the LF index blobs), scripts/new-languages.json. .gitattributes already covers grammars/**/parser.c.

Deliberately not in this PR: treating .cls/.frm/.ctl files as classes (Class node + Methods) — that is the separate draft #2087, stacked on this one so it can be reviewed or declined independently. Also out of scope: .vbs (no header markers), .vbp/.vbg project files, VB.NET (#1073).

Known grammar gaps (lines reported as parse_partial; the files still index): a call with a leading omitted argument (.Add , x), Print #f, …, graphics Line (x, y)-(x2, y2), _-continued comments, and the .frm header Object = "{GUID}…" lines.

With the grammar in place VB6 files no longer "vanish silently" (the note on #2074), which largely dissolves that follow-up.

Checklist

• Every commit is signed off (git commit -s)
• Tests pass locally — run on Windows with a zig/clang toolchain without ASan/UBSan (no sanitiser runtime on this host): language discover extraction grammar_regression grammar_labels lang_contract → 737 passed, 0 failed, 2 Windows platform skips; repro_language_registry repro_call_node_manifest repro_call_argument_matrix_b → 58 passed; repro_invariant_breadth → PASS (vb6 calls=1 callable=1 module=0); bash tests/test_language_count_contract.sh → 163 grammars, 7 surfaces OK. CI's sanitised runs are the authoritative check.
• Lint: clang-format-20 --dry-run --Werror clean on every touched src/ and internal/cbm file; cppcheck not run locally (not installed) — relying on CI
• New behaviour is covered by tests (listed above); all fixtures are synthetic

[github-actions]

Thanks for opening this — it has been seen, and it is queued.

This note is automated, but it is not a brush-off: it exists so you know where your PR stands instead of having to guess from silence.

Current review status: working through a backlog. 0.9.1-rc.1 is out, so the release freeze that held reviews is over — but it left a large queue of open pull requests behind it, and we are reading through them oldest-first. The background is in discussion #1144.

What that means for this PR, concretely:

• It will not be closed for inactivity. No stale bot touches pull requests here.
• It may still sit a while before a human reads it. That is on us, not on you.
• Older PRs are read first, so a recent one is not being skipped — it is behind a queue.

Things that will genuinely speed it up whenever review does happen:

• Keep it rebased on main — the tree is moving quickly right now, and a conflicting branch cannot be reviewed as the diff you intended.
• Get CI green, or say which failures you believe are pre-existing.
• Keep the change to one claim. Bundled features and refactors get split before they get merged, which costs you a round trip.
• Every commit needs a sign-off (git commit -s) — CI enforces DCO.

If this fixes a bug, a reproduction we can run is worth more than a description of the symptom.

Thanks for contributing, and sorry in advance for the wait.