fix(queue): confirm submission and terminal turns before advancing (#43)

[MarsLuay]

Summary

• Require a confirmed matching user turn before a queued command is treated as submitted, so an ignored send click can no longer skip or complete that prompt.
• Bind response waiting to that command's user/assistant turn and treat idle gaps, delayed generation, errors, interrupts, and waiting-for-user as non-terminal until the bound assistant turn is confirmed.
• Persist per-command delivery metadata for worker recovery, keep popup idle-wait starts working, and cover the ⚡ Optimize getFallbackMessages by combining querySelectorAll calls #25-docs: expand installation and contribution guides #33 fixture plus restart/skip/duplicate cases.

Test plan

• npm run check (tests, ESLint, typecheck)
• Load the unpacked extension, start a multi-command sequence, and confirm command N+1 is not injected while command N is still streaming/researching
• Ignore or cancel a send and confirm the current command stays in the queue (completedCount does not increase)
• Restart the service worker mid-send and after confirmed submission; confirm no duplicate send and no dropped prompt
• Start a popup sequence while ChatGPT is already generating and confirm it still waits for idle first

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