feat: structured fact store for cross-session memory persistence

[luceinaltis]

Summary

• Add FactStore (DuckDB) that persists TradeThesis objects across sessions with automatic supersession handling (new thesis on same ticker → old one marked as superseded)
• Wire write path: ConversationEngine._persist_facts() upserts thesis after each query — zero additional LLM calls since data is already structured in AnalysisResult.trade_thesis
• Wire read path: StandardHandler injects open theses as prior_thesis evidence into analysis loop; QuickPathHandler appends thesis reminder to price checks; session-start briefing shows open theses with upcoming catalysts

Motivation

The existing 3-tier memory system (JSONL → Markdown → DuckDB FTS) discards structured data at write-time then attempts to reconstruct it from free-text at read-time. TradeThesis (ticker, entry_zone, target, stop, conviction, catalyst_date) exists as a perfect dataclass at runtime but was never persisted. This PR solves that with deterministic SQL lookup as the primary retrieval path, keeping BM25+vector search as fallback.

Validated by supermemory's ASMR research: structured fact extraction at write-time + deterministic lookup beats vector search for temporal/contradiction/update scenarios.

Files changed

File	Change
qracer/memory/fact_models.py	New — PersistedThesis, Finding, SessionDigest, ThesisStatus dataclasses
qracer/memory/fact_store.py	New — DuckDB CRUD with supersession, catalyst date parsing, ticker-based lookup
qracer/conversation/engine.py	Add fact_store param + _persist_facts() write path
qracer/conversation/handlers.py	StandardHandler: inject prior theses; QuickPathHandler: thesis reminder
qracer/conversation/quickpath.py	generate_briefing() shows open theses with upcoming catalysts
qracer/cli.py	Initialize FactStore, wire to engine and briefing
qracer/memory/__init__.py	Add new exports
tests/memory/test_fact_store.py	New — 15 unit tests (CRUD, supersession, catalyst parsing)
tests/conversation/test_engine.py	3 new integration tests (persistence, supersession, graceful degradation)
.gitignore	Fix !qracer/memory/ exception for post-flatten layout

Test plan

• pytest tests/memory/test_fact_store.py — 15 passed
• pytest tests/conversation/test_engine.py — 55 passed (40 existing + 15 new)
• Full suite: 724 passed (3 pre-existing Windows codec failures, CI on Linux)
• ruff check + ruff format clean
• CI (code-quality + test-suite + docs-validation)

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