feat: drawer witness flag inline-edit (T72.3)

Memories grow per-flag witness checkboxes (you / host / guest) that
auto-submit on change via HTMX. The new POST route emits a manual_edit
event with target_kind=memory_witness and a {flag, value} payload;
prior_value mirrors the same shape so an inverse edit restores the
flag. The drawer's recent-memories query now selects the three
witness columns alongside the existing fields so the template can
render checkbox state without a second query per row.

chat/state/manual_edit.py

@@ -24,6 +24,12 @@ T72.1 (Phase 2.5) adds one list-shaped edit:
   by string equality so the route handler doesn't have to track fact
   indices across re-renders.
 
+T72.3 adds a per-flag witness toggle:
+- ``memory_witness`` — flip one of ``witness_you`` / ``witness_host`` /
+  ``witness_guest`` on a memory row. Payload's ``new_value`` is a dict
+  ``{"flag": "you"|"host"|"guest", "value": 0|1}`` and ``prior_value``
+  mirrors the same shape so an inverse edit can restore the flag.
+
 Pin toggles intentionally use the existing ``memory_pin_changed`` event
 (registered in :mod:`chat.state.memory`) rather than ``manual_edit`` so
 the projection writes both ``pinned`` and ``auto_pinned`` atomically.
@@ -37,6 +43,8 @@ from sqlite3 import Connection
 from chat.eventlog.log import Event
 from chat.eventlog.projector import on
 
+_VALID_WITNESS_FLAGS = {"you", "host", "guest"}
+
 
 def _clamp(value: int, lo: int, hi: int) -> int:
     return max(lo, min(hi, value))
@@ -120,5 +128,15 @@ def _apply_manual_edit(conn: Connection, e: Event) -> None:
                     target_id["target_id"],
                 ),
             )
+    elif kind == "memory_witness":
+        # T72.3: toggle one of the three witness flags on a memory row.
+        # ``new_value`` is the dict ``{"flag", "value"}``; ``prior_value``
+        # mirrors the same shape so an inverse edit restores the flag.
+        flag = new_value["flag"]
+        if flag in _VALID_WITNESS_FLAGS:
+            conn.execute(
+                f"UPDATE memories SET witness_{flag} = ? WHERE id = ?",
+                (1 if int(new_value["value"]) else 0, int(target_id)),
+            )
     # Unknown target_kind: silently no-op for v1. Future kinds (activity
     # fields, etc.) extend the dispatch above.