fix(auth): ask for a fresh proof before the record or a credential to it leaves

Exporting the whole record, making a clinician share link, minting a token,
and the admin backup download, upload and restore, data wipe and password
reset ran on a live session alone. The plaintext full backup did, while the
encrypted one beside it asked for a second factor. Whoever held a stolen
session could take the record, or leave behind a credential that outlives
the session.

These now go through one gate, requireRecentProof (assertRecentCookieProof
for the routes that resolve their caller themselves). A browser session
passes after a sign-in or re-proof within five minutes: a second factor on
an account that has one, otherwise the password or a passkey. The refusal is
401 auth.reproof.required with meta.methods, and the web opens the re-proof
dialog, posts the proof to the new POST /api/auth/reproof and retries. A
password proof stamps the new Session.reproofAt (migration 0359), never
mfaVerifiedAt, so it cannot stand in for a second factor anywhere.

On Bearer, the full backup asks for an X-Step-Up elevation; the encrypted
export asks for a second-factor elevation on an account that has one. Share
links and connector tokens keep taking the token alone, because the shipped
app calls them without an elevation and reads a 401 there as a dead
session; the guard test names them.

Key rotation keeps its stricter second-factor gate.

src/lib/openapi/error-codes.ts

@@ -62,6 +62,7 @@ export const ERROR_CODE_CATALOGUE: Readonly<Record<string, readonly string[]>> =
       "auth.refresh.revoked",
       "auth.reproof.failed",
       "auth.reproof.required",
+      "auth.reproof.too_weak",
       "auth.scope.insufficient",
       "auth.stepup.required",
       "auth.token.expired",