Mobile: make thread archiving one-swipe and recoverable

[Feighery89]

Problem

On mobile, archiving a thread is not a one-gesture action on current servers, and recovering an archived thread requires leaving the thread list for Settings. The older swipe-to-archive attempt in #2045 is closed, conflicted, and did not include an inline recovery path.

Proposed mobile behavior

• Full-swipe any active or settled row to archive it. Snoozed rows keep full-swipe Wake.
• Keep lifecycle actions (Settle, Snooze, Un-settle) plus Archive/Delete in the long-press menu.
• Add an Archived (N) shelf at the bottom of the thread list, collapsed by default and hidden when empty.
• Scope archived results to the current environment/project/search, matching the active list.
• Full-swipe an archived row to restore it; long-press offers Restore/Delete.
• Keep the existing full archive screen for larger histories, with an inline View all link after the first 10 rows.

I would avoid a persistent setting for this: the collapsed, empty-hidden shelf provides point-of-use optionality without adding configuration or permanent list clutter.

[neocody]

Adding independent iOS alpha feedback: a user could not discover the existing archive path at all and reasonably concluded that mobile archiving did not exist. That is useful confirmation that the current thread-screen/Settings route is not discoverable enough. Please treat this as support for an explicit archive action in the conversation list (swipe and/or long-press/overflow) plus recovery near the list, as proposed here.