TUI: show other-directory sessions in /resume picker

[nicklisac]

The resume picker previously listed only sessions from the current working directory, so following up on a session from another project required knowing its id. It now lists current-directory sessions first, then an "Other Directories" section with every other session, each prefixed by its slim working directory.

Description

• Current-directory sessions are listed first (newest-first), followed by an "Other Directories" divider and all other sessions (also newest-first).
• Rows use compact relative ages (now / 5m ago / 2h ago / yesterday / 3d ago / else Jun 19). The model name is shown last so it truncates before the title, and the picker panel is widened to fit.
• The "Other Directories" divider is a non-selectable row: up/down skip it and clicking it does nothing.
• Resuming a session from a different directory appends the target directory to the confirmation toast, e.g. Resumed session: abc (~dir).

User experience

Resuming a session from another project no longer requires knowing its id or path — one grouped list with compact timestamps and a clearly separated "Other Directories" section.

Manual validation

1. Run uv run tau in a directory that has sessions, then open /resume.
2. Confirm current-directory sessions are listed first.
3. With sessions present elsewhere, confirm they appear under "Other Directories" with a slim path on the left.
4. Use up/down to confirm the divider is skipped and Enter selects the highlighted session; clicking the divider does nothing.
5. Resume a foreign-directory session and confirm the toast shows (~path).

Checks

• uv run pytest
• uv run ruff check .
• uv run ruff format --check .
• uv run mypy

Screenshots

This PR was written by me with the assistance of Qwen 3.8 27B UD-Q8_K_L using Tau.