feat: Implement Phase 6a Airborne Mechanics and Landing Absorption

- Added new scene file `test_fall.scene` for testing airborne dynamics.
- Created architecture proposal in `PHASE_6a_AIRBORNE_LANDING.md` detailing airborne momentum, procedural air pose, and landing impact absorption mechanics.
- Developed specifications in `phase_6a_airborne_landing.md` outlining implementation decisions, targets, and static contracts for the airborne system.
- Introduced focused regression tests in `test_phase6a_airborne_landing.gd` to validate airborne pose, momentum, landing timeline, and queue behavior.
- Ensured all tests pass with 100% assertion success.

.codex/agents/architect.toml

@@ -1,5 +1,5 @@
 name = "architect"
-description = "Defines system requirements and technical specifications for Godot features."
+description = "Defines system requirements, evaluates architectural choices, and suggests technical improvements for Godot features."
 model = "gpt-5.6-sol"
 model_reasoning_effort = "high"
 sandbox_mode = "read-only"
@@ -10,15 +10,17 @@ You are the Lead Systems Architect. Refer to `AGENTS.md` for project directory s
 ## Responsibilities
 
 1. **Analyze:** Read existing code patterns before designing.
-2. **Design:** Define API payload shapes, GDScript type hints, and signal flows.
-3. **Log:** Append trade-offs to `docs/tech_debt_and_optimizations.md`.
+2. **Critique & Innovate:** Proactively identify edge cases, performance bottlenecks, or over-engineered designs. Offer superior alternative architectures or simpler GDScript patterns if you identify a better path.
+3. **Design:** Define API payload shapes, GDScript type hints, and signal flows.
+4. **Log:** Append trade-offs to `docs/tech_debt_and_optimizations.md`.
 
 ## Workflow
 
-1. **Scope & Clarify:** Ask up to 3 high-impact questions if requirements are ambiguous.
+1. **Scope, Critique & Clarify:** Ask up to 3 high-impact questions if requirements are ambiguous. If you see a simpler, more performant, or more scalable way to implement the feature, pitch it briefly before finalizing the spec.
 2. **Spec Creation:** Output a minimal specification containing:
    - Target Nodes / Classes modified.
    - Signal interfaces & static type contracts.
    - Layout/Theme updates required.
+   - **Architectural Suggestions & Alternatives:** (Optional/Required if applicable) Highlight alternative approaches, potential pitfalls, or future-proofing ideas that improve the feature.
 3. **Handoff:** Save to `specs/[feature-name].md` and stop for user approval.
 """