test(conftest): kill CCB tmux daemons leaked by subprocess ccb calls

[SevenX77]

Problem

Tests under test/test_v2_phase2_entrypoint.py invoke the ccb CLI via subprocess.run. That subprocess starts the CCB keeper, which wraps itself in an independent tmux daemon whose socket lives under tmp_path/.ccb/ccbd/tmux.sock or /run/user/$UID/ccb-runtime/tmux-*.sock.

The in-process app.shutdown() these tests run at teardown cannot reach the daemons that were started in a separate subprocess. Consequence: each such test leaks ≥1 tmux: server process. On a developer workstation running the test suite repeatedly, dozens of orphaned tmux daemons accumulate in ps, consuming memory and PIDs.

Observed on a dev box: pytest-of-sevenx/pytest-52,57,58 each held 25+ orphaned tmux: server with ETIME over 2 hours before cleanup.

Fix

Two autouse fixtures in test/conftest.py:

• _cleanup_ccb_tmux_per_test (per-test scope): after each test, kills any .ccb/ccbd/tmux.sock daemon found under the test's own tmp_path (safe because tmp_path is exclusive per-test), plus any socket that newly appeared in /run/user/$UID/ccb-runtime/ during the test. The "newly appeared" check is a snapshot diff before/after yield, so existing user sockets in that dir are not touched.
• _cleanup_ccb_tmux_session_end (session scope, belt-and-suspenders): after the whole pytest session, sweeps the pytest base tmp and the runtime dir diff in case any per-test cleanup was missed due to a fixture exception.

Missing tmux binary raises FileNotFoundError and is silently ignored (e.g. Windows CI where tmux is unavailable). Hung kill-server (subprocess timeout after 5s) is logged at WARNING level — loud enough to notice but not fatal. No bare except: / no silent error swallowing.

Dependencies added to conftest.py imports: glob, logging, subprocess (standard library only).

Tests

• Verified on test_ccb_v2_project_lifecycle (real-adapter lifecycle test that definitely spawns the keeper subprocess): zero tmux: server processes remain on the host after the test run. Baseline before this patch: ≥1 per such test run.
• No modifications to any production code.
• No modifications to any existing test.

Scope

Test infrastructure only. Does not change runtime behavior of CCB. Does not modify any lib/ code. A single file touched: test/conftest.py (+63 lines, 0 deletions). No new test files.

Rollback

Single commit, revert with git revert if needed.