Add external IPO history to heat model

Request:
- Add historical data around T0.5 margin heat and rebuild the model.

Changes:
- Add external_ipo_history to store third-party historical IPO records separately from true T0.5 market-heat snapshots.
- Add scripts/archive_ipohk_history.py to archive ipohk structured listed IPO history.
- Archive 807 ipohk rows, including final oversubscription, one-lot win rate, grey-market return, and first-day return where available.
- Extend the v0 analysis dataset with true T0.5 market-heat columns and separate external final-heat columns.
- Rebuild reports/2026-06-15_analysis_model_v0.md with T0.5 coverage and external final-heat calibration.
- Add a Chinese report explaining why historical final oversubscription cannot be treated as T0.5 margin snapshots.
- Update analyst and archivist skills to keep T0.5 and external final history separate.

Verification:
- .venv/bin/python -m py_compile scripts/build_analysis_dataset.py scripts/archive_ipohk_history.py scripts/archive_t0_5_market_heat.py
- .venv/bin/python scripts/build_analysis_dataset.py --as-of 2026-06-15T19:20:00Z
- Python sqlite3 PRAGMA integrity_check returned ok and foreign_key_check returned zero rows.
- Confirmed 807 external_ipo_history rows, 792 rows with external final oversubscription, 5 true T0.5 market-heat rows, and 297 analysis dataset rows.
- git diff --cached --check

Next useful context:
- True T0.5 historical backtesting still requires ongoing frozen margin-heat snapshots during each IPO subscription window.

schema/hk_ipo.schema.sql

@@ -74,6 +74,36 @@ CREATE TABLE IF NOT EXISTS ipo_market_heat (
   UNIQUE (ticker, provider, observed_at)
 );
 
+CREATE TABLE IF NOT EXISTS external_ipo_history (
+  history_id TEXT PRIMARY KEY,
+  ticker TEXT NOT NULL,
+  provider TEXT NOT NULL,
+  source_id TEXT NOT NULL,
+  stock_name TEXT,
+  listing_date TEXT,
+  price_range_low_hkd REAL,
+  price_range_high_hkd REAL,
+  issue_price_hkd REAL,
+  one_lot_capital_hkd REAL,
+  one_hand_win_rate_pct REAL,
+  public_oversubscription_times REAL,
+  total_fundraise_hkd_b REAL,
+  market_cap_at_listing_hkd_b REAL,
+  grey_market_return_pct REAL,
+  first_day_return_pct REAL,
+  sponsor TEXT,
+  source_date TEXT,
+  archived_at TEXT NOT NULL,
+  local_path TEXT NOT NULL,
+  url TEXT NOT NULL,
+  file_sha256 TEXT,
+  notes TEXT,
+  UNIQUE (ticker, provider, listing_date),
+  CHECK (local_path NOT LIKE '/%'),
+  CHECK (local_path NOT LIKE './%'),
+  CHECK (local_path NOT LIKE '%\%')
+);
+
 CREATE TABLE IF NOT EXISTS price_performance (
   performance_id TEXT PRIMARY KEY,
   ticker TEXT NOT NULL REFERENCES ipo_master(ticker),