The dashboard's dedicated memory-provider UI (4b184cbe5) excluded
memory.provider from /api/config/schema server-side. Desktop's settings
page builds its field list from that schema, so the Memory Provider
dropdown silently vanished from Desktop after v0.18.1.
- web_server.py: restore memory.provider as a select in _SCHEMA_OVERRIDES,
with options built from plugins.memory discovery (was a stale hardcoded
[builtin, honcho] list before the removal)
- plugins/memory: add list_memory_provider_names() — directory-scan-only
name listing, safe at module import time (no provider imports)
- web ConfigPage: hide memory.provider client-side instead — the Plugins
page owns the dedicated provider-switching UI there
- tests: schema contract (select present, category memory, builtin
sentinel) + invariant that every discoverable provider is selectable
861d69c7bb