feat: smart tool output filtering for token savings (M26)

[bug-ops]

Summary

• Add command-aware output filter pipeline in ShellExecutor that compresses tool output before context insertion
• OutputFilter trait with OutputFilterRegistry (first-match-wins dispatch)
• sanitize_output() strips ANSI escapes and progress bars on all output
• 5 built-in filters: test (failures-only), git (compact stats), clippy (group by rule), dir listing (noise removal), log dedup (normalize+count)
• Configurable via [tools.filters] in config

Token Savings Estimates

Filter	Scenario	Savings
Test	Green suite (200 tests)	94-99%
Git diff	Large diff	80-99%
Clippy	20+ warnings	70-90%
Log dedup	Repetitive logs	70-85%
Dir listing	With target/node_modules	50-70%
ANSI strip	All output	5-15% baseline

Test plan

• 1418 unit tests pass (20 new filter tests)
• Clippy zero warnings
• Security audit: no ReDoS, bounded HashMap (10K cap), zero info loss on errors
• Performance audit: all O(n), LazyLock regexes, no hot-path compilation
• Code review: all 4 issues fixed (dead metrics removed, HashMap cap, test gaps filled, match tightened)

Closes #426, closes #427, closes #428, closes #429, closes #430, closes #431, closes #432, closes #433