feat(smolmachines): provision_ca + provision_git + provision_supervise (PRD 0023 chunk 4d)

End-to-end provisioning parity with the docker backend. After this
chunk a smolmachines bottle has a working trust store, git-gate
gitconfig, and supervise MCP registration — same shape as docker,
dispatched via `smolvm machine cp` / `smolvm machine exec` instead
of `docker cp` / `docker exec`.

Adds three new provision modules:
- ca.py:        select egress vs pipelock CA (same logic as
                docker), machine cp + update-ca-certificates,
                log sha256 fingerprint.
- git.py:       copy host .git when --cwd was passed; render
                ~/.gitconfig with insteadOf URLs. URL prefix is
                `git://<bundle_ip>:9418/...` (no DNS in the
                TSI-allowlisted guest) vs docker's
                `git://git-gate/...`.
- supervise.py: `claude mcp add` via machine_exec; URL is
                `http://<bundle_ip>:9100/`. Failure is logged but
                non-fatal (matches docker).

Shared render: `render_git_gate_gitconfig` moves out of
backend/docker/provision/git.py into the platform-neutral
claude_bottle/git_gate.py (renamed to git_gate_render_gitconfig
for consistency with the existing git_gate_render_* helpers),
parameterized on a `gate_host` argument so both backends use the
same logic with different addresses.

Path/user fixups for the post-chunk-4c agent image (real
claude-bottle image, USER node, $HOME=/home/node):
- prompt.py default path moves from /root/... to
  /home/node/.claude-bottle-prompt.txt; chown + chmod after
  machine cp.
- skills.py default skills dir moves from /root/.claude/skills to
  /home/node/.claude/skills; chown -R per skill.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

claude_bottle/git_gate.py

@@ -35,7 +35,7 @@ from pathlib import Path
 from typing import Mapping
 
 from .log import die
-from .manifest import Bottle
+from .manifest import Bottle, GitEntry
 
 
 # Short network alias for git-gate inside the sidecar bundle. The
@@ -140,6 +140,35 @@ def git_gate_aggregate_extra_hosts(
     return merged
 
 
+def git_gate_render_gitconfig(
+    entries: tuple[GitEntry, ...], gate_host: str
+) -> str:
+    """Render the agent's ~/.gitconfig content for git-gate
+    `insteadOf` rewrites. Pure host-side, no docker / smolvm;
+    exposed for tests + reuse across backends.
+
+    `gate_host` is the part of the URL between `git://` and the
+    repo path — backends differ here:
+      - docker:        `git-gate` (the short network alias)
+      - smolmachines:  `<bundle_ip>:<port>` (no DNS in the
+                       TSI-allowlisted guest)
+
+    Empty `entries` returns an empty string so callers can no-op
+    cleanly without conditional formatting at the call site."""
+    if not entries:
+        return ""
+    out = [
+        "# claude-bottle git-gate (PRD 0008): every git operation against\n",
+        "# a declared upstream routes through the gate, which mirrors\n",
+        "# the upstream bidirectionally (gitleaks-scanned push;\n",
+        "# fetch-from-upstream-before-every-upload-pack via access-hook).\n",
+    ]
+    for entry in entries:
+        out.append(f'[url "git://{gate_host}/{entry.Name}.git"]\n')
+        out.append(f"\tinsteadOf = {entry.Upstream}\n")
+    return "".join(out)
+
+
 def git_gate_known_hosts_line(host: str, port: str, key: str) -> str:
     """Format `host[:port] key` for OpenSSH's known_hosts. Non-default
     ports use the bracketed `[host]:port` form (the form OpenSSH writes