[plan-13] Grammar / Parser Fidelity — tree-sitter parse coverage + custom-grammar loading

Defect

The structural-parsing layer (tree-sitter, powering smart_outline / smart_unfold and observation parsing) has two correctness gaps that share a root: the grammar/query contract is not validated against the languages it claims to support. Plain .js / .mjs / .cjs became unparseable when a shared JS/TS query started referencing TS-only node types that the tree-sitter version rejects (a realized regression of #1654), and smart_outline / smart_unfold never load the custom grammars declared in .claude-mem.json. The fix is a grammar contract: queries must parse against every declared language version, and custom-grammar configuration must actually be honored, both enforced in CI.

Children

• #2750 — v12.6.0: plain .js/.mjs/.cjs unparseable — realized regression of #1654 (tree-sitter rejects TS-only node types in the shared jsts query)
• #2773 — smart_outline / smart_unfold never load custom grammars from .claude-mem.json

Fix sequence

1. Split the shared JS/TS query so plain-JS files never hit TS-only node types; pin the query to the installed grammar version.
2. Wire .claude-mem.json custom-grammar declarations into the smart_outline / smart_unfold load path.
3. Add a CI matrix that parses representative files for every declared language + custom grammar; a query/grammar mismatch fails CI.

Test matrix

Language	Source	Required behavior
JS	.js / .mjs / .cjs	parses without TS-only node-type errors
TS/TSX	.ts / .tsx	parses (no regression)
custom	.claude-mem.json grammar	loaded and used by smart_outline/unfold

Out of scope

Observer output fidelity (plan-11); data persistence (plan-09).