Add Phase 8: polish, docs, clippy fixes, README, benchmark

[montfort]

Summary

• Doc comments with executable examples on all public API items (T052-T054)
• Fix 6 clippy warnings: collapsible_if, if_same_then_else, needless_range_loop (T055)
• All 160 tests pass with --all-features (T056)
• README.md with installation, usage, feature flags, contributing guide (T058)
• Performance benchmark: 1041-line fixture, 44 functions, median 67ms < 100ms (T059)
• Minimal feature build: 3.2s < 30s (T061)
• speckit.analyze fixes: spec status Draft→Implemented, US4 acceptance scenario for include_methods, Cargo.toml categories, comments-only and non-UTF-8 edge-case tests

Test plan

• cargo test --all-features — 160 tests passing
• cargo clippy --all-features -- -D warnings — clean
• Doc tests compile and run (cargo test --doc)
• Performance benchmark < 100ms (median 67ms)
• Minimal build < 30s (3.2s)

🤖 Generated with Claude Code

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