[FEATURE] Multi-select and bulk archive in the Claude Code session list (mobile app / claude.ai/code)

### Problem

The Claude Code session list (mobile app "Code" tab, claude.ai/code, desktop) accumulates
one entry per local session that ever registered with the bridge. On my machine this adds
up fast: ~100-190 new `claude` sessions per day across interactive terminals, `claude -p`
runs from scripts/hooks, and sessions created from the phone through `claude remote-control`.
Yesterday I had to clean up **129 stale `localhost-*` entries**.

Archiving them is currently a **one-by-one** operation: open the row's overflow menu, tap
Archive, wait for the list to re-render, repeat. 129 times. There is no way to select a
range, and no "archive everything older than X" / "archive all disconnected" escape hatch.
The only practical workaround I found was scripting `POST /v1/code/sessions//archive`
from the browser console, which obviously is not something a normal user will do.

### Request

**Multi-select + bulk archive in the session list**, on the mobile app first (that is where
the list is least manageable) and ideally on claude.ai/code and desktop too:

1. Long-press (mobile) / shift-click or a "Select" affordance (web) enters a selection mode.
2. Tapping further rows toggles them; a range select would be even better.
3. A toolbar action archives all selected sessions in one call, with a single undo.
4. Bonus: a "Select all matching current filter" checkbox, so `filter: disconnected` +
select all + archive becomes a two-tap cleanup.

### Related

- #93870 — filter the session list by connection state (connected vs disconnected). That
filter plus bulk archive is what actually makes the list maintainable; either one alone
is half a solution.
- #87877 — auto-archive / programmatic cleanup of disconnected sessions.
- #74682 — auto-archive for scheduled-task run sessions.
- #81299 — re-registering under the same name should replace the old entry.

### Environment

Claude Code 2.1.266-2.1.270 on macOS 15 (darwin 24.6.0), Android mobile app, claude.ai/code.