docs: drop ssh from README/example, supersede PRD 0007 (PRD 0009)

- README architecture diagram drops the socat/ssh image box and
  the agent's ~/.ssh/config; the prose-bullets section drops the
  ssh image; the manifest example swaps `ssh:` for `git:` so
  someone copy-pasting it picks up the new shape.
- claude-bottle.example.json: `default` bottle's `"ssh": []` is
  gone (now just an empty bottle); the gitea-dev example already
  uses `git:` since the ExtraHosts work.
- PRD 0007 carries a "Superseded by PRD 0009" header at the top
  with a one-paragraph block explaining why; the file stays so
  the rationale of the prior design is still in-tree.
- git_gate.py: drop the now-stale shadow-route mention from a
  docstring (the validator went away in the manifest layer).

claude-bottle.example.json

@@ -2,7 +2,6 @@
   "bottles": {
     "default": {
       "env": {},
-      "ssh": [],
       "egress": {
         "allowlist": [
           "github.com",