[Flotapponnier]

port main's MCP and privacy work to dev, before a merge can undo it

Preparing the dev to main merge, the conflict triage turned up one file
group where dev is not ahead but behind, and behind on a leak.

src/lib/mcp-tools.ts and the MCP route exist on both branches and were
written independently, so they conflict as add/add. main's copies carry five
commits dev never received: a thousandfold error and a 35k-token catalogue
(#2764), the search endpoint handing back an API key it had been asked to
search for (#2766), two tools that answered nothing (#2765), a third
annotation the submission scan reads (#2768), and a chain name outranking
the subject of the question (#2770).

Measured rather than inferred from the titles: redact appears 7 times in
main's mcp-tools.ts and 3 times in its route, and 0 times in either of dev's.
Resolving those conflicts in dev's favour, which a bulk resolution would do,
reintroduces the leak.

Checked before overwriting: the dev-to-main diff is additive. main adds
category-aware scoring, a minimum score that cuts prefix-only noise, and
redactSecrets(); the only lines it removes are the ones it replaces. dev
holds nothing in these files that main lacks.

The privacy page is the same shape without the security edge: main's is 219
lines against dev's 140 and is alone in documenting retention and the Vercel
dependency. dev's predates it, from when the page existed only because the
app directory requires a policy URL.

Doing this now, in its own change, means the merge no longer has a
resolution that can silently restore a credential leak.

Gates: tsc clean, eslint clean, 567 tests (up from 561: main's test file
carries six more).