fix(memory): instruct in-turn consolidation + retry on overflow (#41755)

* fix(memory): make overflow errors instruct in-turn consolidation + retry

When bounded memory is full, the add/replace overflow errors now explicitly
tell the model to consolidate (merge/remove/shorten) and retry the write in
the same turn, matching the documented behavior. The replace-overflow path
now also echoes current_entries + usage for parity with add-overflow, so the
model has the same context to act on.

Closes #23378 (working-as-documented; this sharpens runtime to match docs).

* fix(memory): broaden overflow remediation hint beyond 'stale'

Say 'stale or less important' — entries don't have to be stale to be the
right ones to drop when making room.

website/docs/user-guide/features/memory.md

@@ -128,7 +128,7 @@ When you try to add an entry that would exceed the limit, the tool returns an er
 ```json
 {
   "success": false,
-  "error": "Memory at 2,100/2,200 chars. Adding this entry (250 chars) would exceed the limit. Replace or remove existing entries first.",
+  "error": "Memory at 2,100/2,200 chars. Adding this entry (250 chars) would exceed the limit. Consolidate now: use 'replace' to merge overlapping entries into shorter ones or 'remove' stale or less important entries (see current_entries below), then retry this add — all in this turn.",
   "current_entries": ["..."],
   "usage": "2,100/2,200"
 }