fix(sqlite): fall back to journal_mode=DELETE on NFS/SMB/FUSE (#22043)

SQLite's WAL mode requires shared-memory (mmap) coordination and fcntl
byte-range locks that don't reliably work on network filesystems. Upstream
documents this explicitly:
  https://www.sqlite.org/wal.html#sometimes_queries_return_sqlite_busy_in_wal_mode

On NFS / SMB / some FUSE mounts / WSL1, 'PRAGMA journal_mode=WAL' raises
'sqlite3.OperationalError: locking protocol' (SQLITE_PROTOCOL). Before
this change, every feature backed by state.db or kanban.db broke silently:
  - /resume, /title, /history, /branch returned 'Session database not
    available.' with no cause
  - gateway logged the init failure at DEBUG (invisible in errors.log)
  - kanban dispatcher crashed every 60s, driving the known migration race
    (duplicate column name: consecutive_failures, #21708 / #21374)

Changes:
  - hermes_state.apply_wal_with_fallback(): shared helper that tries WAL
    and falls back to DELETE on SQLITE_PROTOCOL-style errors with one
    WARNING explaining why
  - hermes_state.get_last_init_error() + format_session_db_unavailable():
    capture the init failure cause and surface it in user-facing strings
    (with an NFS/SMB pointer for 'locking protocol')
  - hermes_cli/kanban_db.connect(): use the shared helper
  - gateway/run.py: bump SessionDB init failure log DEBUG -> WARNING
    (matches cli.py's existing correct behavior)
  - cli.py (4 sites) + gateway/run.py (5 sites): replace bare
    'Session database not available.' with format_session_db_unavailable()

Tests: 12 new tests in tests/test_hermes_state_wal_fallback.py + 1 new
test in tests/hermes_cli/test_kanban_db.py. Existing suites (state,
kanban, gateway, cli) remain green for all tests unrelated to pre-existing
failures on main.

Evidence: real-world user on NFSv3 mount (172.26.224.200:d2dfac12/home,
local_lock=none) reporting 'Session database not available.' on /resume;
'locking protocol' appears in 4 distinct log entries across backup,
kanban, TUI, and CLI paths in the same session.

closes #22032

gateway/run.py

@@ -1218,7 +1218,13 @@ class GatewayRunner:
             from hermes_state import SessionDB
             self._session_db = SessionDB()
         except Exception as e:
-            logger.debug("SQLite session store not available: %s", e)
+            # WARNING (not DEBUG) so the failure appears in errors.log — matches
+            # cli.py's handling of the same init path.  Users hitting NFS-mounted
+            # HERMES_HOME silently lost /resume, /title, /history, /branch, and
+            # session search without this.  The underlying cause (usually
+            # "locking protocol" from NFS) is now also captured by
+            # hermes_state.get_last_init_error() for slash-command error strings.
+            logger.warning("SQLite session store not available: %s", e)
 
         # Opportunistic state.db maintenance: prune ended sessions older
         # than sessions.retention_days + optional VACUUM. Tracks last-run
@@ -10374,7 +10380,8 @@ class GatewayRunner:
     def _disable_telegram_topic_mode_for_chat(self, source: SessionSource) -> str:
         """Cleanly disable topic mode for a chat via /topic off."""
         if not self._session_db:
-            return "Session database not available."
+            from hermes_state import format_session_db_unavailable
+            return format_session_db_unavailable()
         chat_id = str(source.chat_id or "")
         if not chat_id:
             return "Could not determine chat ID."
@@ -10412,7 +10419,8 @@ class GatewayRunner:
         if source.platform != Platform.TELEGRAM or source.chat_type != "dm":
             return "The /topic command is only available in Telegram private chats."
         if not self._session_db:
-            return "Session database not available."
+            from hermes_state import format_session_db_unavailable
+            return format_session_db_unavailable()
 
         # Authorization: /topic activates multi-session mode and mutates
         # SQLite side tables. Unauthorized senders (not in allowlist) must
@@ -10626,7 +10634,8 @@ class GatewayRunner:
         session_id = session_entry.session_id
 
         if not self._session_db:
-            return "Session database not available."
+            from hermes_state import format_session_db_unavailable
+            return format_session_db_unavailable()
 
         # Ensure session exists in SQLite DB (it may only exist in session_store
         # if this is the first command in a new session)
@@ -10670,7 +10679,8 @@ class GatewayRunner:
     async def _handle_resume_command(self, event: MessageEvent) -> str:
         """Handle /resume command — switch to a previously-named session."""
         if not self._session_db:
-            return "Session database not available."
+            from hermes_state import format_session_db_unavailable
+            return format_session_db_unavailable()
 
         source = event.source
         session_key = self._session_key_for_source(source)
@@ -10757,7 +10767,8 @@ class GatewayRunner:
         import uuid as _uuid
 
         if not self._session_db:
-            return "Session database not available."
+            from hermes_state import format_session_db_unavailable
+            return format_session_db_unavailable()
 
         source = event.source
         session_key = self._session_key_for_source(source)