feat: compression profiles — aggressive/balanced/conservative with per-session config

[ranxianglei]

Summary

• Three compression profiles: aggressive (short tasks), balanced (default), conservative (long experiments)
• Per-session config files at ~/.config/opencode/acp-status/{sessionId}.json — no race conditions
• set_compression_profile tool for model-driven profile switching
• Profile affects: Normal hint, summary limit (100/200/400), compress frequency (4/6/10), large output threshold (2K/5K/10K)

Changes (7 files)

• NEW lib/compress/profile.ts (110 lines): Profile definitions, session config read/write, tool factory
• MOD lib/config.ts: Added compressionProfile config option
• MOD lib/config-validation.ts: Validated new config key
• MOD lib/prompts/system.ts: buildSystemPrompt(profile) generates profile-specific text
• MOD lib/hooks.ts: Resolves effective profile per session at runtime
• MOD lib/compress/index.ts: Re-exports
• MOD index.ts: Tool registration

Test

typecheck ✅, 496 tests pass ✅, build ✅ (333KB)