feat(review): set up Crafter.Review's pre-push review

Crafter.Review reviews a frozen commit range before it is pushed: the
approach, a static proof of the code's bugs, and every claim in the
messages and in the documentation the range changes, one claude process
per lens and unit, or per whole-range pass, and the owner approves the
exact frozen hash before the push. This sets it up for this repository.

.review-gates/config.json turns on three lenses in the commits mode, at
xhigh: repo-better-solution, repo-bug-prover and repo-facts. The
functional lens is off: it exercises a web application through a
browser, and this repository's product is a command-line tool. The
security lens is off by the owner's ruling: crafter-build stores no
secret of its own, and while its Flatpak runs with the user's SSH agent
(--socket=ssh-auth) and the whole host filesystem (--filesystem=host),
everything it runs is code its user chose to run. The rules CI keeps
around its token and signing key go to the approach lens's section
instead.

gate0 lists the commands run by hand before a freeze. build.sh comes
first, because bin/crafter-build compiles project.cpp against the
interfaces it was bootstrapped with, and lint comes after the self-host
build, because lint's AST rules parse with the module PCMs a build
leaves and lint builds only the std PCM itself.

.review-gates/lenses/ holds this repository's section of each lens's
charter, appended to the text Crafter.Review ships: that AGENTS.md is
absent from the frozen tree, the layers and the consumers of
interfaces/, the execution contexts a bug can hide in, where libc++ and
clang are readable from the review's sandbox, and what a "passes the
suite" claim traces to.

The /prepush skill that crafter-review init writes stays untracked. It
is generated from the installed Crafter.Review and refreshed by every
init, so a committed copy would lag the binary it describes. One init
per checkout restores it, which AGENTS.template.md now says, together
with the rules freeze holds every commit of a range to: signed
(requireSigned), with the owner's address as its author and committer
(authors), and no AI attribution trailer (aiTrailers forbid).

.review-gates/config.json

@@ -0,0 +1,28 @@
+{
+  "base": "origin/master",
+  "rangeFrom": "upstream",
+  "authors": [
+    "jorijnvdgraaf@catcrafts.net"
+  ],
+  "aiTrailers": "forbid",
+  "requireSigned": true,
+  "lensSections": ".review-gates/lenses",
+  "modes": {
+    "commits": {
+      "kind": "commits",
+      "lenses": [
+        "repo-better-solution",
+        "repo-bug-prover",
+        "repo-facts"
+      ],
+      "effort": "xhigh"
+    }
+  },
+  "gate0": [
+    "./build.sh",
+    "./bin/crafter-build",
+    "./bin/crafter-build test",
+    "./bin/crafter-build format --check",
+    "./bin/crafter-build lint"
+  ]
+}