feat: v0.1 tree-sitter complexity gate with Claude Code and Codex hooks

[ElbertePlinio]

Closes #1

What changed

• Cargo workspace: complexity-gate-core (tree-sitter parsing, per-language decision/depth/naming tables, config resolution, Git changed-span math) and the complexity-gate CLI (check, hook claude|codex, init, doctor --coverage).
• Languages: JS, TS, TSX, Svelte (script + template), Dart, Rust, Python, Go. Golden fixtures with reference numbers (ESLint/Oxlint, radon, gocyclo, lizard; Dart/Svelte hand-derived) and a two-sided strictness test.
• Hooks: Claude Code PostToolUse/Stop and Codex equivalents, loop guard (3 blocks per session, UNRESOLVED after), state under ~/.pickforge/complexity-gate/.
• Repo gates: CI (test, clippy -D warnings, llvm-cov floor, self-gate, gitleaks, osv-scanner), cargo-dist release workflow, branch protection.
• docs/spec.md is the contract; docs/hooks.md records the harness mapping.

Tested

• cargo test --workspace --locked --all-targets, cargo clippy --workspace --all-targets -- -D warnings, cargo run -- check crates (self-gate), cargo llvm-cov — see CI.
• End-to-end: a real Claude Code session (Stop hook blocked a 21-branch function; agent stopped to ask because the refactor was forbidden) and a real Codex session with hook trust (PostToolUse feedback drove a refactor until the gate passed).
• Real-repo scans: pickscribe, pickforge, pickgauge (legacy violations reported; --changed scopes them out).
• Review: serious-backend class — correctness (two rounds), tests/ops, security/deps. All P0–P2 fixed; see adjudication below.

Not tested

• Release artifacts on macOS/Windows/aarch64 (first tag run will prove them); Windows hook execution.
• Codex hooks in interactive mode (verified with --dangerously-bypass-hook-trust in exec; interactive requires the one-time trust prompt).

Known risks / decisions

• Rust match arms and loop count (stricter than clippy's cognitive metric by design; recorded in spec).
• Repo .complexity-gate.json is trusted like any repo file; tests.exempt is restricted to lines, max_blocks clamped, and a changed config is flagged in the report.
• Deferred: release workflow permission scoping (release.yml: scope contents:write to the release job #2).
• Dismissed with rationale: SHA-pinning of actions (workspace uses version tags); --changed <paths> resolves paths relative to cwd like any CLI; config resolves nearest-to-file (supports nested packages).

Local-review risk class: serious backend.