feat: add session archive/unarchive support to TUI

[B67687]

Issue for this PR

Closes #13964

Type of change

• New feature

What does this PR do?

Adds session archive/unarchive support to the TUI:

• /archive slash command to archive current session
• Session list shows archived sessions when toggled with Tab
• Selecting an archived session unarchives it
• Auto-navigate home when current session is archived
• session_archive keybind (configurable)

This is arebased version of PR #13961 by @uriva, updated to current dev to resolve conflicts that accumulated after the March rebase.

How did you verify your code works?

Rebased onto current dev - used the same conflict resolution approach that worked before. Typecheck passes (at least for the changed opencode package).

Screenshots / recordings

N/A - no UI changes, only keybinds and list filtering.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search results, I found the following related PRs:

Potential Related PRs:

1. PR feat: add session archive/unarchive support to TUI #13961 - "feat: add session archive/unarchive support to TUI"

   • feat: add session archive/unarchive support to TUI #13961
   • Relationship: This is the original PR that the current PR (22372) is a rebase of. The current PR explicitly mentions it's "a rebased version of PR feat: add session archive/unarchive support to TUI #13961 by @uriva, updated to current dev to resolve conflicts."

2. PR feat(app): view archived sessions & unarchive #15250 - "feat(app): view archived sessions & unarchive"

   • feat(app): view archived sessions & unarchive #15250
   • Relationship: Addresses similar functionality for viewing and unarchiving sessions, though appears to be app-focused rather than TUI-focused.

3. PR feat(session): add archive undo + unarchive command #16212 - "feat(session): add archive undo + unarchive command"

   • feat(session): add archive undo + unarchive command #16212
   • Relationship: Related feature for archive undo and unarchive command functionality.

4. PR fix: --continue should skip archived sessions #22174 - "fix: --continue should skip archived sessions"

   • fix: --continue should skip archived sessions #22174
   • Relationship: Bug fix related to handling archived sessions, which is relevant to the archive feature being added.

The current PR (22372) is explicitly a rebase of PR #13961, so they address the exact same feature but at different points in time.