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/manifest.py

@@ -45,7 +45,7 @@ from pathlib import Path
 from typing import Mapping, cast
 
 from .log import die, warn
-from .yaml_subset import parse_frontmatter
+from .yaml_subset import YamlSubsetError, parse_frontmatter
 
 
 def _empty_str_dict() -> dict[str, str]:
@@ -832,6 +832,8 @@ def _load_bottles_from_dir(bottles_dir: Path) -> dict[str, Bottle]:
             fm, _body = parse_frontmatter(path.read_text())
         except OSError as e:
             die(f"could not read {path}: {e}")
+        except YamlSubsetError as e:
+            die(f"{path}: {e}")
         unknown = set(fm.keys()) - _BOTTLE_KEYS
         if unknown:
             allowed = ", ".join(sorted(_BOTTLE_KEYS))
@@ -867,6 +869,8 @@ def _load_agents_from_dir(
             fm, body = parse_frontmatter(path.read_text())
         except OSError as e:
             die(f"could not read {path}: {e}")
+        except YamlSubsetError as e:
+            die(f"{path}: {e}")
         unknown = set(fm.keys()) - _AGENT_KEYS
         if unknown:
             allowed = ", ".join(sorted(_AGENT_KEYS))