fix(mcp): rebuild the prompt prefix when the connector set changes

The `## MCP servers` table lives inside the frozen system prefix, which
PrefixCache holds for twenty idle minutes. Refreshing a user's global-access
snapshot fixed what `mcp.tools()` offers but left the table describing the
world before the change, so an admin could enable a connector, ask for it in an
open conversation, and be told in good faith that it does not exist — with the
tools sitting right there. Same gap on a reinstall, whose new
llm_short_description reached the runtime and not the prompt.

Both refreshes now call `invalidate_prefixes()` on the live contexts they were
already iterating, the seam the skill tools use. Order matters and runs against
the intuition: `render_mcp_list` renders the runtime's in-RAM state, not the
DB, so the invalidation goes last — after the snapshot refresh and after the
servers restart. Rebuild earlier and the prefix is repopulated from the very
descriptions being replaced, with nothing left to invalidate it a second time.
In the reinstall that means waiting out a dependency install; those users were
already reading a stale table, and an early rebuild would only freeze the stale
one in place.

Also warn when a feed's connector.json and index disagree on the integer
version. The manifest silently wins, so if the index is the lower of the two
the strict `feed > installed` comparison is false forever: the connector never
offers an Update and nothing anywhere says why.

docs/projects.md

@@ -73,4 +73,3 @@ Access changes apply immediately — no need for the other person to log out.
 - A private project is simply a project with one member (you). Share it later whenever you want.
 - Renaming a project does not move its folder, so links and the assistant's context keep working.
 - Deleting a project removes its folder for everyone — there is no undo.
-- The assistant may offer to **keep a history** of the project: a trail of snapshots you can look back on, or return to if something goes wrong. If you accept, it notes that in the project's `SKALD.md` and saves a new snapshot whenever the project reaches a meaningful milestone. The history lives inside the project folder on the server (it is powered by git, but you never need to touch it).