fix(popup): keep draining the port backlog after a handler throws

[xgreenx]

A caller handler that threw during the backlog drain lost the rest of the backlog while later port values still arrived, breaking REQ-POPUP-MSG-03/04 and REQ-POPUP-CONT-02/06.

Changes

• Drain survives a throw (ts/packages/popup/src/port.ts:261): a finally requeues the rest in a fresh microtask, still ahead of the port's tasks. The exception propagates untouched.
• Handoff kept: the requeue runs only while this carrier still owns the port, so a handler that detaches hands the rest on.
• Backlog test (port.test.ts:382): two throws, values delivered in order before the port's queued value. Fails on main.
• Detach-then-throw test (port.test.ts:424): the rest goes to the next owner, one exception, no further delivery.
• Bounded harness (port.test.ts:80): runs captured microtasks and fails on a self-requeueing loop instead of hanging.

Verified

• pnpm test in ts/packages/popup: 156/156 pass. On main's port.ts, the backlog test fails, 1 of 21.
• Dropping the ownership check from the finally fails the detach test with "microtasks never settle".
• pnpm typecheck (popup), pnpm lint and pnpm fmt:check (ts) pass. Lint keeps one pre-existing info in packages/ceremony.

Not verified / known issues

• No browser e2e run.
• Microtasks a handler queued before it threw now run between backlog values. Port values still follow the whole backlog.

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