fix(sharing): the Revoke note says a new invite lets the member back, but it is refused#1974

The Revoke confirmation in a Shared Case tells the Owner the revoked teammate "would need a new invite", but a new invite cannot bring the same installation back: the join is refused as already a member.

Steps

1. As Owner, revoke a member from Members.
2. Read the dialog's note: "Recorded in your Manifest as member-revoke. Cannot be undone; they would need a new invite."
3. Create a new invite and have the revoked installation use it.

Expected: what the note says, or a note that says the installation cannot rejoin. Actual: the join is refused as already-member. The roster keeps the revoked installation, and both the join handshake and addMember refuse any installation or key already on it, revoked or not.

Where this sits in the code, and why it was kept out of the change that found it

• Copy: revokeNote in src/renderer/components/sharing/memberModel.ts:270-271.
• Refusal: src/main/services/sharing/joinHandshake.ts:138-145 and src/main/services/sharing/membership.ts:216-231 (the comment there: "An installation or key already on the roster, revoked or not, is already-member: the verifier defines no second member-add for one installation").
• Found by the reviewer pre-pass on the Shared Cases docs PR (#1973), which now says the same installation cannot rejoin. Kept out of that PR because it is docs-only, and out of the entry-points PR (#1972) because the fix is a choice the maintainer owns: correct the copy, or let a revoked installation rejoin, which the verifier does not allow today.