CL-8792: allow-once no longer stalls a second destructive command without re-prompt

[TheGreatAxios]

Implements CL-8792 on the single-slot overlay host.

What changes:

• Settling allow-once resolves exactly once and frees the host, draining pending so the next gate opens.
• A replaceable command surface (help/settings/MCP/etc.) on screen yields to a newly raised decision gate and returns after that gate settles.
• A queued card takes the host before a deferred slash/settings/MCP surface; its auto-deny timer arms only on display.
• Inline popups (mentions, palette, pickers) keep their stacking contracts; a slash requested while a live gate holds the host still waits.
• A pending tool row does not advance elapsed while a decision gate is outstanding but hidden.
• Allow Once still persists nothing; Allow Always / Reject ranking unchanged. Fail-closed preserved (unknown to deny, no-listener emit to deny, Esc to deny). mintGrant, grant reconciliation, and auto-mode rules untouched.

Verification:

• bun run typecheck: exit 0
• bun test src/permission src/tui/gate-wire.test.ts src/tui/request-approval.test.ts: 606 pass, 0 fail, exit 0
• bun test ./src ./tests ./evals ./scripts --randomize --seed 424242: 8036 pass, 0 fail, exit 0
• bun run lint: exit 0
• Red run failed first (9 allow-once-reprompt tests, overlay never reopened / evaluations hung); green passes after the fix.

Flagging warden review: this touches the permission-gate overlay path (gate-wire, overlay host suspend/resume). Do not merge without warden review.

Fixes CL-8792

[linear-code]

CL-8792