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core: the dispatch-hints layer it used to ride with is superseded by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>

hooks/hooks-codex.json

@@ -0,0 +1,17 @@
+{
+  "hooks": {
+    "SessionStart": [
+      {
+        "matcher": "compact",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "\"${PLUGIN_ROOT}/hooks/run-hook.cmd\" session-start-codex",
+            "async": false,
+            "timeout": 30
+          }
+        ]
+      }
+    ]
+  }
+}