fix: pattern project scoping, decay, and dismiss_pattern tool

[CalebisGross]

Summary

• Project scoping: Pattern embedding search now filters by project in SQL instead of post-hoc filtering that leaked cross-project patterns into project-scoped recalls
• Decay fix: Self-sustaining immunity now requires evidence health ratio >= 0.5 (patterns with all-archived evidence no longer stay at strength 1.0 forever). Evidence-based decay applies regardless of access recency. Added fading→archived transition at strength < 0.05
• dismiss_pattern tool: New MCP tool (Fix memory pipeline quality: ranking, LLM gating, decay, noise suppression #22) to archive stale/irrelevant patterns. Backed by new ArchivePattern store method
• ListPatterns expanded: Now returns both active and fading patterns so the decay loop can process fading→archived transitions

Test plan

• All existing tests pass (agent, store, MCP, reactor, dreaming)
• Tool count test updated from 21 to 22
• make build && make check clean
• Full go test ./... green

Fixes #306

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