fix(codex): restore Superpowers after compaction

Codex re-fires SessionStart with source "compact" after every context
compaction; the summary keeps progress but sheds the bootstrap and any
active skill's instructions — measured July cause of post-compaction
dispatch drift in long SDD runs (with re-injection: 18/18 hook fires,
66/66 post-compaction dispatch tuples correct in a 12.4h stress run).
Codex discovers skills natively at startup, so the hook is silent
there: the compact re-fire is the one unowned lifecycle point.

Adds the plugin-provided hook (hooks-codex.json + session-start-codex,
compact-only, fails open), wires it into the manifest and package,
documents install/trust behavior, updates codex-tools.md with the
re-grounding fallback, and tests the hook lifecycle, manifest, and
archive contents.

Rebuilt from the July codex-spinout-fixes branch, pared to the hook
core: the dispatch-hints layer it used to ride with is superseded by
the merged 2059-2062/2077-2080 stack and is dropped.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.codex-plugin/plugin.json

@@ -21,7 +21,7 @@
     "workflow"
   ],
   "skills": "./skills/",
-  "hooks": {},
+  "hooks": "./hooks/hooks-codex.json",
   "interface": {
     "displayName": "Superpowers",
     "shortDescription": "Planning, TDD, debugging, and delivery workflows for coding agents",