feat(git-gate+orchestrator): slice 13c(i) — per-bottle git-gate provisioning render

The consolidated gateway serves every bottle's repos under /git/<bottle_id>/
(slice 10), so each bottle's bare repos + per-repo credential config must be
provisioned into that namespace. This adds the renderer for that; placing
the creds + running it inside the gateway is the launch-wiring step.

- Extract the credential-wiring `init_repo` shell into a shared
  `_git_gate_init_repo_fn(repo_root, creds_dir)` — one source for the
  security-sensitive logic. The single-tenant daemon entrypoint is
  byte-unchanged (still /git + /git-gate/creds; existing tests green).
- git_gate_render_provision(bottle_id, upstreams): posix-sh that inits ONE
  bottle's bare repos under /git/<bottle_id>/ reading creds from
  /git-gate/creds/<bottle_id>/. Init-only (no `git daemon` — the shared
  gateway already serves). Isolating each bottle's repo root + creds dir by
  id is what keeps one bottle's push credentials out of another's repos.
- bottle_id is embedded unquoted in the script, so it's restricted to a
  shell/path-safe alphabet (registry ids are token_hex; defense in depth).

pyright 0 errors; pylint 9.83/10; unit suite green (1724 tests; the 13
test_sidecar_init /bin/sleep errors are pre-existing NixOS-local noise).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WBMWTEtQdJ4W5UrWuLHCck

bot_bottle/git_gate.py

@@ -46,6 +46,7 @@ from .git_gate_render import (
     git_gate_known_hosts_line,
     git_gate_render_access_hook,
     git_gate_render_entrypoint,
+    git_gate_render_provision,
     git_gate_render_gitconfig,
     git_gate_render_hook,
     git_gate_upstreams_for_bottle,
@@ -155,6 +156,7 @@ __all__ = [
     "git_gate_render_gitconfig",
     "git_gate_known_hosts_line",
     "git_gate_render_entrypoint",
+    "git_gate_render_provision",
     "git_gate_render_hook",
     "git_gate_render_access_hook",
     "provision_git_gate_dynamic_keys",