refactor(egress): write routes.yaml as actual YAML, not JSON-in-yml

`egress_render_routes` now emits hand-rolled YAML in the same style
as `pipelock_render_yaml`. The egress addon parses it via
`yaml_subset.parse_yaml_subset` — the same parser the manifest
loader + pipelock_apply use.

Why bother: routes.yaml is bind-mounted into the egress sidecar
AND surfaced to operators through `routes edit` (PRD 0019). JSON-
in-yml renders ugly in $EDITOR and signals "this is data" rather
than "this is config you can read at a glance". Real YAML reads
cleanly.

Mechanics:

  - `yaml_subset.py` drops its `claude_bottle.log` dependency.
    Errors now raise `YamlSubsetError` (a `ValueError`); the
    manifest loader + pipelock_apply catch it at the boundary
    and forward to `die` / `PipelockApplyError` so callers see
    the same behavior they did before.
  - `Dockerfile.egress` adds one COPY line for `yaml_subset.py`
    so it sits flat in `/app/` next to the addon. The addon
    uses an absolute-import-with-fallback shim so the same file
    works inside the container AND from the host's unit tests.
  - `egress_apply._merge_single_route` round-trips current
    routes.yaml through `parse_yaml_subset` + a new
    `_render_routes_payload` helper instead of `json.loads` +
    `json.dumps`.

End-to-end: rebuilt the egress image, ran `./cli.py start` to a
full bring-up, confirmed the addon's boot log shows `egress:
loaded 9 route(s)` — i.e., the YAML parses inside the container.
453 unit + 3 integration tests pass.

claude_bottle/yaml_subset.py

@@ -59,7 +59,20 @@ from __future__ import annotations
 import re
 from dataclasses import dataclass
 
-from .log import die
+
+class YamlSubsetError(ValueError):
+    """Raised when input violates the YAML subset's rules. Callers
+    that want fatal-exit semantics (manifest loader, pipelock-apply,
+    etc.) catch this at their own boundary and forward to `die`;
+    callers running outside the claude-bottle CLI process (the
+    egress sidecar's addon) handle it as a normal exception."""
+
+
+def die(msg: str) -> None:
+    """Module-local helper so the parser body reads cleanly. Just
+    raises YamlSubsetError — the `claude-bottle: error: ` prefix
+    is added by the boundary `die` in `claude_bottle.log`."""
+    raise YamlSubsetError(msg)
 
 
 # --- Tokenizer / line preprocessing ----------------------------------------