4 fixes from Gemini Code Assist PR #1689 review:
1. HIGH: Multi-part message content duplication — skip array-content
messages instead of joining+replacing all text parts with compressed
result, which caused content duplication (e.g., [A,B] → [comp(A+B), comp(A+B)])
2. HIGH: String.prototype.replace $& vulnerability — use arrow function
callback instead of string arg in restorePreservedBlocks() to prevent
special replacement patterns ($&, , etc.) from corrupting restored
content containing code, URLs, or file paths
3. HIGH: UI/backend rule name mismatch — ALL_CAVEMAN_RULES in
CompressionSettingsTab.tsx now uses actual backend rule names
(polite_framing, hedging, verbose_instructions, etc.) instead of
fabricated names (hedging_disclaimer, redundant_please, etc.)
that would break the skip-rules feature
4. MEDIUM: Remove no-op turn_marker rule — pattern /^$/g matches only
empty strings and replaces with empty string, achieving nothing.
Removed from CAVEMAN_RULES; total count now 29 (was 30).
Tests: 72/72 pass, typecheck: 0 errors, lint: 0 errors
