feat(plane): budget metering (task 2)

MeteredClient wraps a ChatClient, sums the provider's usage rows per call,
prices them from a Model manifest's parameters (cache-hit, input, output per
million), and raises BudgetExhausted before a call once the usd or calls
ceiling is reached. A 401/402 or "Insufficient Balance" failure becomes
AccountError with the provider's message. An unpriced model reports usd None,
never zero, and refuses a usd budget; summary() gives the spend block of a
task's summary.json.

The two plane modules are registered as spec-owned in the module audit (their
consumers land in tasks 3-4) and the audit manifest is regenerated.

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

src/openultrasast/model/audit.py

@@ -54,6 +54,8 @@ SPEC_OWNED = {
     "cpg": "model-grounded-detection Req 4: the CPG seam package",
     "cpg.backend": "model-grounded-detection Req 4.1/4.5: the single Joern subprocess boundary",
     "cpg.capability": "model-grounded-detection Req 4.2/4.3: the engine probe that degrades to suspicion",
+    "plane": "ai-service-plane Req 1-4: the service plane package; runner and reconciler integration in tasks 3-4",
+    "plane.budget": "ai-service-plane Req 2.3/2.4: metered chat client with usd and calls ceilings; task integration in tasks 3, 6",
 }
 
 STANDALONE = {