Bootstrap HK IPO historical archive

Request:
- Use the project archivist workflow to update historical IPO data.

Changes:
- Add an embedded SQLite archive at data/hk_ipo.sqlite.
- Add schema/hk_ipo.schema.sql and scripts/bootstrap_historical_data.py for reproducible archive generation.
- Archive HKEXnews source PDFs for 06658, 06675, and 06106 under repo-relative data/raw paths.
- Export Git-friendly snapshots for ipo_master, offering_terms, ipo_demand, source_refs, and data_gaps.
- Add .gitignore rules for Python cache and SQLite transient files.

Verification:
- Re-ran the bootstrap script successfully.
- Ran PRAGMA integrity_check on the SQLite database.
- Verified source_refs paths are repo-relative, files exist, and SHA-256 hashes match.
- Verified snapshot row counts match SQLite table counts.
- Ran git diff --check and searched generated durable files for machine-specific absolute paths.

schema/hk_ipo.schema.sql

@@ -0,0 +1,83 @@
+PRAGMA foreign_keys = ON;
+
+CREATE TABLE IF NOT EXISTS ipo_master (
+  ticker TEXT PRIMARY KEY,
+  company_name_en TEXT NOT NULL,
+  company_name_zh TEXT,
+  stock_short_name TEXT,
+  exchange TEXT NOT NULL DEFAULT 'HKEX',
+  board TEXT NOT NULL DEFAULT 'Main Board',
+  status TEXT NOT NULL,
+  listing_date TEXT,
+  application_start_date TEXT,
+  application_end_date TEXT,
+  allotment_results_expected_date TEXT,
+  industry_label TEXT,
+  data_as_of TEXT NOT NULL,
+  notes TEXT
+);
+
+CREATE TABLE IF NOT EXISTS offering_terms (
+  ticker TEXT PRIMARY KEY REFERENCES ipo_master(ticker),
+  source_id TEXT NOT NULL,
+  prospectus_date TEXT,
+  offer_price_hkd REAL,
+  board_lot INTEGER,
+  min_subscription_amount_hkd REAL,
+  global_offer_shares INTEGER,
+  hk_offer_shares_initial INTEGER,
+  international_offer_shares_initial INTEGER,
+  public_offer_pct_initial REAL,
+  over_allotment_offer_shares INTEGER,
+  offer_size_adjustment_offer_shares INTEGER,
+  market_cap_hkd_m REAL,
+  gross_proceeds_hkd_m REAL,
+  net_proceeds_hkd_m REAL,
+  issued_shares_upon_listing INTEGER,
+  data_as_of TEXT NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS ipo_demand (
+  demand_id TEXT PRIMARY KEY,
+  ticker TEXT NOT NULL REFERENCES ipo_master(ticker),
+  source_id TEXT NOT NULL,
+  stage_date TEXT NOT NULL,
+  valid_applications INTEGER,
+  successful_applications INTEGER,
+  public_oversubscription_times REAL,
+  international_placees INTEGER,
+  international_oversubscription_times REAL,
+  final_hk_offer_shares INTEGER,
+  final_international_offer_shares INTEGER,
+  data_as_of TEXT NOT NULL,
+  notes TEXT
+);
+
+CREATE TABLE IF NOT EXISTS source_refs (
+  source_id TEXT PRIMARY KEY,
+  ticker TEXT NOT NULL REFERENCES ipo_master(ticker),
+  source_type TEXT NOT NULL,
+  title TEXT NOT NULL,
+  path_base TEXT NOT NULL DEFAULT 'repo_root',
+  local_path TEXT NOT NULL,
+  url TEXT NOT NULL,
+  file_sha256 TEXT,
+  source_date TEXT,
+  archived_at TEXT NOT NULL,
+  notes TEXT,
+  CHECK (path_base = 'repo_root'),
+  CHECK (local_path NOT LIKE '/%'),
+  CHECK (local_path NOT LIKE './%'),
+  CHECK (local_path NOT LIKE '%\%')
+);
+
+CREATE TABLE IF NOT EXISTS data_gaps (
+  gap_id TEXT PRIMARY KEY,
+  ticker TEXT NOT NULL REFERENCES ipo_master(ticker),
+  stage TEXT NOT NULL,
+  field_name TEXT NOT NULL,
+  reason TEXT NOT NULL,
+  expected_resolution_date TEXT,
+  created_at TEXT NOT NULL,
+  notes TEXT
+);