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/backend/docker/pipelock_apply.py

@@ -23,7 +23,7 @@ import tempfile
 from pathlib import Path
 
 from ...pipelock import pipelock_render_yaml
-from ...yaml_subset import parse_yaml_subset
+from ...yaml_subset import YamlSubsetError, parse_yaml_subset
 from .bottle_state import pipelock_state_dir
 from .pipelock import pipelock_container_name
 
@@ -110,7 +110,10 @@ def fetch_current_allowlist(slug: str) -> str:
     line — the operator-facing format for the TUI / agent's
     current-config mount."""
     yaml = fetch_current_yaml(slug)
-    cfg = parse_yaml_subset(yaml)
+    try:
+        cfg = parse_yaml_subset(yaml)
+    except YamlSubsetError as e:
+        raise PipelockApplyError(f"running pipelock yaml: {e}") from e
     hosts = cfg.get("api_allowlist", [])
     if not isinstance(hosts, list):
         raise PipelockApplyError(
@@ -136,7 +139,10 @@ def apply_allowlist_change(
     new_hosts = parse_allowlist_content(new_allowlist_content)
     container = pipelock_container_name(slug)
     current_yaml = fetch_current_yaml(slug)
-    cfg = parse_yaml_subset(current_yaml)
+    try:
+        cfg = parse_yaml_subset(current_yaml)
+    except YamlSubsetError as e:
+        raise PipelockApplyError(f"running pipelock yaml: {e}") from e
     current_hosts = cfg.get("api_allowlist", [])
     if not isinstance(current_hosts, list):
         raise PipelockApplyError(