feat(stats): record snapshots on SessionEnd

[ousamabenyounes]

Fixes #716

Summary

• add caveman-stats.js --record for silent SessionEnd snapshots using hook stdin transcript_path and session_id
• wire the SessionEnd recorder through the Claude plugin manifest and standalone installers/uninstallers
• keep malformed/missing hook stdin quiet and avoid guessing a recent session during --record

I kept the caveman-style --all pile output out of this PR so the change stays focused on dense lifetime history.

RED

node tests/test_caveman_stats.js

✗ --record appends SessionEnd snapshot silently from stdin
Expected values to be strictly equal:
+ actual - expected
+ '\nCaveman Stats\n...'
- ''
37 passed, 1 failed

node --test tests/installer/e2e.freshinstall.test.mjs tests/installer/plugin-manifest.test.mjs

not ok ... claude hook install wires SessionEnd stats recorder once
actual: 0
not ok ... plugin manifest wires SessionEnd stats recorder
0 !== 1
# pass 16
# fail 2

Revert proof with implementation files reset to upstream/main and new tests kept:

37 passed, 2 failed
not ok 19 - plugin manifest wires SessionEnd stats recorder
0 !== 1
# pass 16
# fail 3

GREEN

Baseline on upstream/main with repo-local run-ci.sh:

npm test: 112 passed, 0 failed
node tests/test_caveman_stats.js: 37 passed, 0 failed
python3 tests/verify_repo.py: all checks passed
diff-coverage-gate: PASS no changed production lines with coverage data

Final on this branch:

npm test: 115 passed, 0 failed
node tests/test_caveman_stats.js: 39 passed, 0 failed
python3 tests/verify_repo.py: all checks passed
diff-coverage-gate: PASS 100.00% (206/206) changed production lines covered