fix(GATE-PR-SIZE-TEMPDIR): honor caller temporary storage for semantic evidence

Row: GATE-PR-SIZE-TEMPDIR

scripts/check-pr-size.py:913 creates semantic evidence worktrees with dir="/dev/shm". This ignores the caller's TMPDIR and writes into storage that the caller can prohibit. The sanitized child environment also drops temporary-directory selection. Three fixtures in tests/scripts/test_check_pr_size.py repeat the hardcoded directory.

The cleanup finally block skips container removal when git worktree remove raises. This leaves owned temporary files after a failure.

Repair these directly related temporary-storage and cleanup paths. Preserve checker classification, budgets, creation mutation registration, readiness, and semantic evidence acceptance. Prove the actual CLI path red before and green after without writing into /dev/shm. Verify cleanup after successful evidence, refused evidence, and exceptions.

Owner: GATE-PR-SIZE-TEMPDIR, spec .agents/specs/gate-pr-size-tempdir.md. The fresh implementer works on a linked task branch pinned to 2add10f31d28381a10c206596f62cd1878bf7205. Fresh review and the operator gate remain required.

Read .agents/specs/gate-pr-size-tempdir.md and inspect scripts/check-pr-size.py around line 913, then review the three related fixtures in tests/scripts/test_check_pr_size.py. Run the actual CLI path to reproduce the failure without writing into /dev/shm. Done means caller temporary storage is honored, classification and evidence behavior are preserved, and cleanup is verified after success, refusal, and exceptions.