docs: replace stale bash-first framing with Python-stdlib-first

The project started life as bash scripts and got rewritten to Python
(documented in docs/research/bash-vs-python-vs-go.md). Several docs
still carried the old "bash-first" framing — misleading for anyone
reading them now (8.7k lines of Python vs. ~130 lines of bash, all
in scripts/demo*.sh).

- CLAUDE.md "What this is" + "Conventions": orchestrator is Python,
  posture is stdlib-first.
- docs/prds/0010-cred-proxy.md, docs/research/manifest-format-and-
  grouping.md: quoted CLAUDE.md's old wording — re-quote.
- docs/research/built-in-supervisor-design.md, landscape-containerized-
  claude.md, agent-sandbox-landscape.md, pipelock-assessment.md,
  network-egress-guard.md: drop "bash-first" claims about the project,
  keep accurate descriptions of external tools' bash usage.

Leaves untouched: bash code-fence syntax in examples, README's
literal `bash scripts/demo.sh` invocation (the demo IS bash),
Claude Code's "Bash tool" references, IVIJL/devbox bash description
(that project actually is bash), and the bash-vs-python-vs-go
research note that records the rewrite decision.

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

docs/prds/0010-cred-proxy.md

@@ -407,8 +407,8 @@ cannot smuggle a stolen token through this path.
 The proxy binary. Two real options:
 
 - **Python (stdlib)** — `http.server` + `urllib`/`http.client`,
-  no new pip packages. Matches CLAUDE.md's "bash-first, low-deps"
-  posture. SSE pass-through is fiddly but doable.
+  no new pip packages. Matches CLAUDE.md's "Python, stdlib-first,
+  low-deps" posture. SSE pass-through is fiddly but doable.
 - **Go single binary** — cleaner SSE story, smaller runtime,
   one static binary in a scratch/distroless image. New build
   dependency.