Centralize language support and generalize agent packet retrieval

[TheGreenCedar]

Summary

This PR aligns language-support claims across the codebase and removes benchmark-specific shortcuts from production retrieval.

• Shared language registry — codestory-contracts now owns support tiers; the indexer, runtime, CLI, and docs consume that registry instead of maintaining separate claim maps.
• Parser-backed expansion — Kotlin, Swift, Dart, and Bash move to fidelity-gated graph coverage with tree-sitter rules and fixture tests. Go, Ruby, PHP, and C# fidelity suites expand around symbols, imports, member ownership, and receiver/call resolution.
• Generalized packet retrieval — production packet search no longer steers on benchmark-family terms. scripts/lint-retrieval-generalization.mjs guards against benchmark literals in retrieval and indexing paths.
• Sidecar diagnostics — unresolved packet candidates are surfaced to callers and can block packet sufficiency when sidecar evidence exists but cannot be resolved.
• CLI files counts — output separates whole-index, filtered, visible, and truncated totals so filtered views do not look like repository-wide counts.

Receiver/call resolution and agent packet quality remain bounded claims; see docs/architecture/language-support.md for the supported boundary.

Test plan

• cargo fmt --check and cargo check --all-targets
• node scripts/lint-retrieval-generalization.mjs
• cargo test -p codestory-indexer --test fidelity_regression
• cargo test -p codestory-indexer --test tictactoe_language_coverage
• cargo test -p codestory-runtime packet_sufficiency -- --nocapture
• cargo test -p codestory-cli --test cli_golden_path -- --nocapture
• cargo test -p codestory-cli --test onboarding_contracts -- --nocapture
• cargo build --release -p codestory-cli
• Ignored repo-scale e2e stats (CODESTORY_ALLOW_SKIP_REAL_REPO_DRILL_CASES=1)

Repo-scale indexing stats are logged in docs/testing/codestory-e2e-stats-log.md (full-sidecar proof tier, 68.25s index, 238 files, 89,726 nodes).

Notes

• Real-repo drill cases were skipped locally; treat the e2e stats row as indexing evidence, not drill proof.
• HTML, CSS, and SQL remain structural collectors, not semantic code-navigation languages.