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.

tests/unit/test_egress_addon_core.py

@@ -105,16 +105,39 @@ class TestParseRoutes(unittest.TestCase):
 
 
 class TestLoadRoutes(unittest.TestCase):
-    def test_json_text_round_trip(self):
-        routes = load_routes('{"routes":[{"host":"api.example"}]}')
+    def test_yaml_text_round_trip(self):
+        routes = load_routes(
+            'routes:\n'
+            '  - host: "api.example"\n'
+        )
         self.assertEqual(1, len(routes))
         self.assertEqual("api.example", routes[0].host)
 
-    def test_invalid_json_raises_value_error(self):
-        # Both decode and schema errors land as ValueError so callers
-        # have a single except clause.
+    def test_full_route_shape_parses(self):
+        routes = load_routes(
+            'routes:\n'
+            '  - host: "api.example"\n'
+            '    auth_scheme: "Bearer"\n'
+            '    token_env: "EGRESS_TOKEN_0"\n'
+            '    path_allowlist:\n'
+            '      - "/v1/"\n'
+            '      - "/messages"\n'
+        )
+        self.assertEqual(1, len(routes))
+        r = routes[0]
+        self.assertEqual("api.example", r.host)
+        self.assertEqual("Bearer", r.auth_scheme)
+        self.assertEqual("EGRESS_TOKEN_0", r.token_env)
+        self.assertEqual(("/v1/", "/messages"), r.path_allowlist)
+
+    def test_empty_routes_list(self):
+        routes = load_routes("routes: []\n")
+        self.assertEqual((), routes)
+
+    def test_invalid_yaml_raises_value_error(self):
+        # Tab indent is a YamlSubsetError; ValueError is its base.
         with self.assertRaises(ValueError):
-            load_routes("not json at all")
+            load_routes("routes:\n\t- host: x\n")
 
 
 # --- match_route ---------------------------------------------------------