pre-push(17.6): install, Docker wrapper and first-run docs

`ousast pre-push install|uninstall [REPO] [--force] [--docker]` ships in the
wheel with the hook as package data; it honours core.hooksPath, refuses an
existing hook unless --force (which chains it as pre-push.before-ousast), and
uninstall restores the chained hook. ops/ousast-docker is a hook-callable
script: the repository read-only and the artifact directory at their own
paths, stdin passed through, no network, --memory 3g, the GHCR 2.0.1 image by
default, advisory exit unless blocking. Help text for every pre-push flag; a
first-run guide, settings, skip-reason glossary, CI recipe and full --help in
docs/scanning.md; README tiers 1 and 2 pull the published image. The image
was not rebuilt: 1.1 GB free, below the 4 GB threshold. Requirements 7.4, 9.6.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

benchmarks/measurements/2026-09-08-module-audit.json

@@ -1,7 +1,7 @@
 {
-  "modules": 154,
+  "modules": 155,
   "counts": {
-    "load_bearing": 149,
+    "load_bearing": 150,
     "standalone_capability": 5
   },
   "orphaned": [],
@@ -1262,6 +1262,14 @@
         "push.runner"
       ]
     },
+    {
+      "module": "push.install",
+      "classification": "load_bearing",
+      "reason": "reachable from gate, map_gate, pair_gate, cli",
+      "importers": [
+        "cli"
+      ]
+    },
     {
       "module": "push.policy",
       "classification": "load_bearing",