[Refactor] Remove dead code markers and fix all clippy warnings

[oleander]

Context

Currently src/hook.rs and src/bin/hook.rs have #![allow(dead_code)] directives that mask potential dead code warnings. This needs to be removed and all warnings addressed.

Priority

🔴 CRITICAL - Must be done first before other refactoring

Steps

1. Remove dead code suppression

   # Remove this line from both files:
   # src/hook.rs:1
   # src/bin/hook.rs:1
   #![allow(dead_code)]

2. Run clippy to find issues

   cargo clippy --all-targets --all-features

3. Address each warning

   • For unused private items: Delete if truly unused
   • For unused public items: Add documentation explaining their purpose or remove if obsolete
   • Specifically investigate:
     • StringPool struct in hook.rs lines 62-85 (defined but never used)
     • Args struct in hook.rs lines 50-58 (may duplicate bin/hook.rs)
     • Any test helper functions that are obsolete

4. Run automated fixes

   cargo fix --allow-dirty --allow-staged
   cargo clippy --fix --allow-dirty --allow-staged

Verification Criteria

✅ Pass:

• cargo clippy produces ZERO warnings
• cargo test passes all tests
• cargo build --release succeeds
• No #![allow(dead_code)] directives remain (except with explicit justification comments)
• All dead code either removed or documented as intentionally public API

Estimated Time

2-3 hours

Dependencies

None - this should be done first

Labels

• refactor
• technical-debt
• priority: critical