[BUG] Clicking a session row in `claude agents` does nothing since 2.1.271 (fullscreen, macOS Terminal.app)

## Describe the bug

Since 2.1.271, left clicking a session row in the `claude agents` list no longer opens that session. Nothing happens on click. Keyboard navigation (arrows + Enter) still works.

Rolling back to 2.1.270 restores clicking immediately, with the same terminal, settings and sessions. 2.1.272 is still affected.

## Steps to reproduce

1. Set `"tui": "fullscreen"` in `~/.claude/settings.json`
2. Have a few background sessions running
3. Run `claude agents`
4. Left click any session row (Pinned, Ready for review, Working, Completed, etc.)

**Expected:** the clicked session opens, as in 2.1.270.
**Actual:** the click is ignored.

Running `~/.local/share/claude/versions/2.1.270 agents` in the same terminal, against the same sessions, opens rows on click as expected.

## Environment

- Claude Code: broken in 2.1.271 and 2.1.272, works in 2.1.270
- Install: native installer (`~/.local/share/claude/versions`)
- OS: macOS (Darwin 25.5.0)
- Terminal: Apple Terminal.app, `TERM=xterm-256color`, "Use Option as Meta key" enabled
- TUI mode: fullscreen

## Notes

The 2.1.271 changelog mentions adding mouse support to the `/config` panel but no change to the agents view. Comparing the 2.1.270 and 2.1.271 bundles, the session row's own `onClick` looks unchanged, while the shared mouse dispatch changed: the click position is now resolved to a node in a separate step, and a new hover scope / `elementKey` mechanism was added. That shared hit testing change looks like the likely cause, since only clicking regressed.

Workaround: pin 2.1.270 with `DISABLE_AUTOUPDATER=1` and point `~/.local/bin/claude` at the 2.1.270 binary.

Compare the 2.1.270 and 2.1.271 bundles, starting with the shared mouse dispatch, hit testing, hover scope, and elementKey changes noted in the issue, then trace how they reach the agents session rows and their onClick handler. Done means left-clicking any row in fullscreen mode on macOS Terminal.app opens that session while keyboard navigation continues to work.

Written by the indexing model from the issue text.