fix(db): fix migration failures when upgrading from 0.8.0 schema

Migration 1: remove idx_sessions_token_hash from _SCHEMA_STATEMENTS.
The legacy schema has sessions.token (not token_hash). The IF NOT EXISTS
guard only prevents duplicate index names — it still requires the column
to exist. Migration 2 drops and rebuilds sessions with token_hash anyway,
so creating the index in migration 1 was redundant.

Migration 3: replace ALTER TABLE ADD COLUMN with a table rebuild.
SQLite rejects ALTER TABLE ADD COLUMN NOT NULL DEFAULT <expression> when
the table already contains rows. The old DB has ~181k geo_cache rows, so
the ALTER always failed. Rebuild copies existing rows with last_seen set
to cached_at as a reasonable approximation of last-seen time.

backend/app/db.py

@@ -102,10 +102,15 @@ CREATE TABLE IF NOT EXISTS schema_migrations (
 """
 
 # Ordered list of DDL statements to execute on initialisation.
+# NOTE: _CREATE_SESSIONS_TOKEN_INDEX is intentionally omitted here.
+# The old 0.8.0 schema has a `sessions.token` column (not `token_hash`), so
+# running CREATE INDEX … ON sessions (token_hash) in migration 1 would fail
+# with "no such column: token_hash" on legacy databases.  Migration 2 drops
+# and recreates the sessions table with token_hash and also creates the index,
+# so there is no need to create it in migration 1.
 _SCHEMA_STATEMENTS: list[str] = [
     _CREATE_SETTINGS,
     _CREATE_SESSIONS,
-    _CREATE_SESSIONS_TOKEN_INDEX,
     _CREATE_BLOCKLIST_SOURCES,
     _CREATE_IMPORT_LOG,
     _CREATE_GEO_CACHE,
@@ -133,8 +138,24 @@ CREATE UNIQUE INDEX idx_sessions_token_hash ON sessions (token_hash);
     3: """
 -- Migration 3: Add last_seen timestamp to geo_cache for retention policy.
 -- Tracks when each IP was last referenced to enable purging of stale entries.
--- Default to current timestamp for existing rows.
-ALTER TABLE geo_cache ADD COLUMN last_seen TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
+-- SQLite rejects ALTER TABLE ADD COLUMN with a non-constant NOT NULL default
+-- when the table already contains rows, so we rebuild the table instead.
+-- Existing rows receive last_seen = cached_at as a reasonable approximation
+-- (the IP was at least seen when it was first cached).
+DROP TABLE IF EXISTS geo_cache_new;
+CREATE TABLE geo_cache_new (
+    ip              TEXT    PRIMARY KEY,
+    country_code    TEXT,
+    country_name    TEXT,
+    asn             TEXT,
+    org             TEXT,
+    cached_at       TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
+    last_seen       TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'))
+);
+INSERT INTO geo_cache_new (ip, country_code, country_name, asn, org, cached_at, last_seen)
+    SELECT ip, country_code, country_name, asn, org, cached_at, cached_at FROM geo_cache;
+DROP TABLE geo_cache;
+ALTER TABLE geo_cache_new RENAME TO geo_cache;
 """,
     4: """
 -- Migration 4: Add scheduler_lock table for multi-worker safety.

backend/pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "bangui-backend"
-version = "0.9.19-rc.1"
+version = "0.9.19-rc.3"
 description = "BanGUI backend — fail2ban web management interface"
 requires-python = ">=3.12"
 dependencies = [