framework: make tool discoverability, workspace placement and model tiering mechanical

An undocumented tool is, from inside an agent session, indistinguishable from a
tool that was never written. The framework shipped 26 git wrappers and named 6 of
them in its resident index docs — 23% discoverability, with pr-review.sh among the
missing. The observable consequence was an agent obeying Constitution gate 7 as
best it could see it, reaching for raw curl, sending GitHub's APPROVE to a Gitea
host, and getting HTTP 200 with the review silently filed PENDING. Three times.
That is not a discipline failure and no amount of prose fixes it.

Four changes, each converting a rule that decayed into a mechanism that cannot:

- check-tools-index.sh (new, CI-blocking): every tool in an enforced suite must be
  named in a resident index doc, and every tool an index names must exist. The git
  suite is enforced now; other suites report coverage without failing, so the
  ratchet tightens one reviewed PR at a time instead of landing as one sweep. The
  enforced list is framework-owned rather than a marker inside operator-owned
  TOOLS.md — a doc marker would let an operator silence the gate on exactly the
  host where it matters most. Carries --self-test, because a checker that only
  ever passes is indistinguishable from one that is not running.

- TOOLS-REFERENCE.md: complete 28-entry git index, plus the APPROVED/APPROVE
  dialect note that explains why pr-review.sh is not a formality.

- mosaic-worktree.sh + wrapper-guard.sh (upstreamed): the rule "big work goes on a
  work filesystem" already existed in prose, and 255 GB accumulated in $HOME across
  842 directories anyway, under five simultaneous placement conventions on one
  host. The helper therefore exposes no placement decision — given a branch name,
  every path is derived from `git worktree list --porcelain`. Worktrees rather than
  clones because enumerability is the only thing that makes reclaim safe, and
  reclaim is by evidence (clean tree + no unpushed commits), never by size or age.
  The guard blocks three mechanically-detectable mistakes and nothing else:
  a checkout into $HOME, a raw provider-API write to an endpoint that has a
  wrapper, and the literal APPROVE event. Reads pass untouched.

- STANDARDS.md: model tiering as a standard, named by capability class so it
  survives a model generation. Start cheapest, escalate on evidence, benchmark
  before demoting a task class, and keep the class->model binding in operator
  config with the DB-backed config service as the end state.

Registering the guard in runtime/claude/settings.json is the point of upstreaming
it: ~/.claude/settings.json is a framework-managed copy, so a hand-added hook there
is destroyed by the next upgrade. In the template it survives, and it reaches every
host instead of one.

packages/mosaic/framework/runtime/claude/settings.json

@@ -52,6 +52,16 @@
             "timeout": 10
           }
         ]
+      },
+      {
+        "matcher": "Bash",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "~/.config/mosaic/tools/git/wrapper-guard.sh",
+            "timeout": 10
+          }
+        ]
       }
     ],
     "PostToolUse": [