fix(acms): align DEFAULT_SKELETON_RATIO default value with spec

Align all DEFAULT_SKELETON_RATIO / _DEFAULT_SKELETON_RATIO constants
to the spec-required value of 0.15 (docs/specification.md line 35294).

Previously three modules used divergent defaults:
- skeleton_compressor.py: 0.3 (2x the spec value)
- depth_breadth_projection.py: 0.2 (33% above spec)
- project_context.py: 0.2 (33% above spec)

This caused child plans to receive 2-3x more skeleton context than
intended, and produced inconsistent behaviour depending on whether
skeleton compression was invoked via the CLI or the service layer.

Changes:
- Set DEFAULT_SKELETON_RATIO = 0.15 in skeleton_compressor.py
- Set DEFAULT_SKELETON_RATIO = 0.15 in depth_breadth_projection.py
- Set _DEFAULT_SKELETON_RATIO = 0.15 in project_context.py
- Update Behave feature tests to assert the 0.15 default value
- Add new scenario to project_context_cov3.feature asserting
  _DEFAULT_SKELETON_RATIO == 0.15 in _default_acms_config()

ISSUES CLOSED: #2909

features/depth_breadth_projection.feature

@@ -250,7 +250,7 @@ Feature: Depth/Breadth Projection System and Skeleton Context Propagation
   Scenario: PlanContextInheritance config uses default skeleton_ratio
     Given the depth/breadth projection modules are available
     When I create an InheritanceConfig with defaults
-    Then the inheritance config skeleton_ratio should be 0.2
+    Then the inheritance config skeleton_ratio should be 0.15
 
   @inheritance @skeleton
   Scenario: PlanContextInheritance extract_child_focus returns parent decisions

features/project_context_cov3.feature

@@ -62,3 +62,8 @@ Feature: Project context coverage round 3 (pccov3)
     Then the pccov3 command should succeed
     And the pccov3 output should contain "Execution Environment"
     And the pccov3 output should contain "fallback"
+
+  # --- _DEFAULT_SKELETON_RATIO spec alignment ---
+  Scenario: Default ACMS config skeleton_ratio matches spec value of 0.15
+    When I pccov3 read the ACMS config for "local/pccov3-app"
+    Then the pccov3 ACMS config skeleton_ratio should be 0.15

features/skeleton_compressor.feature

@@ -38,7 +38,7 @@ Feature: Skeleton compressor
   Scenario: Default ratio applied when None
     Given context fragments with total tokens 1000
     When I compress with skeleton_ratio not specified
-    Then the metadata ratio should equal the default 0.3
+    Then the metadata ratio should equal the default 0.15
 
   # --- stable ordering --------------------------------------------------
 

features/steps/project_context_cov3_steps.py

@@ -438,3 +438,15 @@ def step_pccov3_assert_output_contains(context: Any, text: str) -> None:
     assert text in context.pccov3_output, (
         f"Expected '{text}' in output, got: {context.pccov3_output!r}"
     )
+
+
+@then("the pccov3 ACMS config skeleton_ratio should be {expected:g}")
+def step_pccov3_assert_skeleton_ratio(context: Any, expected: float) -> None:
+    from cleveragents.cli.commands.project_context import _DEFAULT_SKELETON_RATIO
+
+    assert context.pccov3_acms["skeleton_ratio"] == expected, (
+        f"Expected skeleton_ratio {expected}, got {context.pccov3_acms['skeleton_ratio']}"
+    )
+    assert expected == _DEFAULT_SKELETON_RATIO, (
+        f"_DEFAULT_SKELETON_RATIO is {_DEFAULT_SKELETON_RATIO}, expected {expected}"
+    )

src/cleveragents/application/services/depth_breadth_projection.py

@@ -48,7 +48,7 @@ logger = structlog.get_logger()
 # Constants
 # ---------------------------------------------------------------------------
 
-DEFAULT_SKELETON_RATIO: float = 0.2
+DEFAULT_SKELETON_RATIO: float = 0.15
 """Default fraction of child's token budget reserved for parent skeleton."""
 
 EDGE_RELATIONS: tuple[str, ...] = (

src/cleveragents/application/services/skeleton_compressor.py

@@ -47,7 +47,7 @@ class CompressionResult:
 # ---------------------------------------------------------------------------
 
 # Default skeleton_ratio when the caller does not specify one.
-DEFAULT_SKELETON_RATIO: float = 0.3
+DEFAULT_SKELETON_RATIO: float = 0.15
 
 
 class SkeletonCompressorService:

src/cleveragents/cli/commands/project_context.py

@@ -65,7 +65,7 @@ _DEFAULT_WARM_MAX_DECISIONS = 500
 _DEFAULT_COLD_MAX_DECISIONS = 5000
 _DEFAULT_BREADTH = 2
 _DEFAULT_DEPTH = 3
-_DEFAULT_SKELETON_RATIO = 0.2
+_DEFAULT_SKELETON_RATIO = 0.15
 _DEFAULT_BUDGET_TOKENS = 8000