refactor(manifest): break import cycle by extracting ManifestBottle to a leaf module

manifest.py imported the extends/loader resolvers, while those resolvers
needed ManifestBottle back from manifest.py — a true bidirectional cycle
papered over with in-function imports and TYPE_CHECKING guards (not clear
dependency inversion).

Extract ManifestBottle into a new leaf module manifest_bottle.py that depends
only on the other leaf modules (manifest_util/agent/egress/git/schema).
manifest.py re-exports ManifestBottle, so `from .manifest import ManifestBottle`
callers are unaffected. With the cycle gone:

- manifest_extends and manifest_loader import ManifestBottle from
  manifest_bottle and their other deps from the real source modules, all at
  top level (TYPE_CHECKING block removed).
- manifest.py imports the extends/loader/schema/yaml_subset/log helpers at
  module top; all per-function lazy imports in the cluster are removed.

No behavior change; full unit suite green, pyright clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NkwFXLFff9PYPy4wgVBJp9

bot_bottle/manifest_loader.py

@@ -3,9 +3,10 @@
 from __future__ import annotations
 
 from pathlib import Path
-from typing import TYPE_CHECKING
 
 from .log import warn
+from .manifest_bottle import ManifestBottle
+from .manifest_extends import resolve_bottles
 from .manifest_schema import (
     entity_name_from_path,
     validate_bottle_frontmatter_keys,
@@ -13,9 +14,6 @@ from .manifest_schema import (
 from .manifest_util import ManifestError
 from .yaml_subset import YamlSubsetError, parse_frontmatter
 
-if TYPE_CHECKING:
-    from .manifest import ManifestBottle
-
 
 def check_stale_json(dir_path: Path, md_dir: Path, label: str) -> None:
     """Die if `<dir_path>/bot-bottle.json` exists but `md_dir` does
@@ -78,8 +76,6 @@ def load_bottle_chain_from_dir(
 
     Only the files in the extends chain are read — unrelated bottle files
     are never touched. Raises ManifestError on parse or validation failure."""
-    from .manifest_extends import resolve_bottles
-
     raws: dict[str, dict[str, object]] = {}
     to_load = [bottle_name]
     while to_load: