Add archivist incremental sync state

Request:
Add archivist support for remembering which IPO archive stages have already been synced and which stages should be updated next.

Changes:
- Add sync_runs, ticker_sync_state, sync_tasks, and price_performance tables to the archive schema.
- Add scripts/update_sync_state.py to derive per-ticker stage status and rebuild the next-sync task queue.
- Export the new sync-state tables as Git-friendly CSV snapshots.
- Document the incremental archive flow in the archivist skill and README.

Verification:
- Ran scripts/bootstrap_historical_data.py.
- Ran scripts/update_sync_state.py with a deterministic as-of timestamp.
- Checked SQLite integrity and DB-to-snapshot row counts with Python sqlite3.
- Parsed Python scripts with ast.parse.
- Ran git diff --check and checked for temporary SQLite/cache files.

Next useful context:
- Current derived queue has 2 open tasks for 06658 and 15 waiting_until_due tasks for future stages.

schema/hk_ipo.schema.sql

@@ -53,6 +53,23 @@ CREATE TABLE IF NOT EXISTS ipo_demand (
   notes TEXT
 );
 
+CREATE TABLE IF NOT EXISTS price_performance (
+  performance_id TEXT PRIMARY KEY,
+  ticker TEXT NOT NULL REFERENCES ipo_master(ticker),
+  stage TEXT NOT NULL,
+  source_id TEXT,
+  as_of_date TEXT NOT NULL,
+  open_price_hkd REAL,
+  high_price_hkd REAL,
+  low_price_hkd REAL,
+  close_price_hkd REAL,
+  return_pct REAL,
+  turnover_hkd_m REAL,
+  data_as_of TEXT NOT NULL,
+  notes TEXT,
+  UNIQUE (ticker, stage)
+);
+
 CREATE TABLE IF NOT EXISTS source_refs (
   source_id TEXT PRIMARY KEY,
   ticker TEXT NOT NULL REFERENCES ipo_master(ticker),
@@ -81,3 +98,45 @@ CREATE TABLE IF NOT EXISTS data_gaps (
   created_at TEXT NOT NULL,
   notes TEXT
 );
+
+CREATE TABLE IF NOT EXISTS sync_runs (
+  sync_run_id TEXT PRIMARY KEY,
+  mode TEXT NOT NULL,
+  as_of TEXT NOT NULL,
+  started_at TEXT NOT NULL,
+  finished_at TEXT,
+  status TEXT NOT NULL,
+  notes TEXT,
+  CHECK (status IN ('running', 'complete', 'failed'))
+);
+
+CREATE TABLE IF NOT EXISTS ticker_sync_state (
+  ticker TEXT NOT NULL REFERENCES ipo_master(ticker),
+  stage TEXT NOT NULL,
+  status TEXT NOT NULL,
+  required INTEGER NOT NULL DEFAULT 1,
+  due_date TEXT,
+  completed_at TEXT,
+  last_source_id TEXT,
+  data_gap_id TEXT,
+  last_sync_run_id TEXT REFERENCES sync_runs(sync_run_id),
+  updated_at TEXT NOT NULL,
+  notes TEXT,
+  PRIMARY KEY (ticker, stage),
+  CHECK (status IN ('complete', 'pending_not_due', 'pending_due', 'blocked', 'not_applicable')),
+  CHECK (required IN (0, 1))
+);
+
+CREATE TABLE IF NOT EXISTS sync_tasks (
+  task_id TEXT PRIMARY KEY,
+  ticker TEXT NOT NULL REFERENCES ipo_master(ticker),
+  stage TEXT NOT NULL,
+  task_type TEXT NOT NULL,
+  task_status TEXT NOT NULL,
+  due_date TEXT,
+  data_gap_id TEXT,
+  last_sync_run_id TEXT REFERENCES sync_runs(sync_run_id),
+  updated_at TEXT NOT NULL,
+  notes TEXT,
+  CHECK (task_status IN ('open', 'waiting_until_due', 'blocked'))
+);