feat: integrate llm-connect FR-1/FR-3/FR-4 into IHF bridge

FR-3 (async_execute_prompt): CollectiveProposals now invokes all agents
concurrently via callAgentsBatch → single bridge subprocess with
asyncio.gather. Latency scales with slowest agent, not sum.

FR-4 (BudgetTracker): AgentDelegations passes tokenBudget to bridge;
llm-connect enforces it natively via BudgetTracker in RunConfig.
BudgetExceededError is a first-class BridgeError variant with total/
consumed/requested fields surfaced to the operator.

FR-1 (LLMServer passthrough): bridge accepts optional serverUrl field;
if present, calls POST {serverUrl}/execute instead of spawning a new
adapter. Infrastructure ready for hot-agent pre-warming (no schema
change required).

AgentBridge.hs: adds callAgentsBatch, callAgentWithBudget,
BudgetExceededError constructor, bridgeErrorMessage helper, defaultRequest,
requestToJson. All controllers updated to use bridgeErrorMessage.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Web/Controller/DecisionRecords.hs

@@ -8,7 +8,7 @@ import Web.View.DecisionRecords.Edit
 import Generated.Types
 import IHP.Prelude
 import IHP.ControllerPrelude
-import Application.Helper.AgentBridge (callAgent, checkGovernancePolicy)
+import Application.Helper.AgentBridge (callAgent, checkGovernancePolicy, bridgeErrorMessage)
 import Application.Helper.ModelRouter (resolveAgent)
 import Data.List (intercalate)
 
@@ -227,7 +227,7 @@ instance Controller DecisionRecordsController where
                                 result <- liftIO $ callAgent agent userMsg
                                 case result of
                                     Left err -> do
-                                        setErrorMessage ("Implementation proposal failed: " <> err.errorMessage)
+                                        setErrorMessage ("Implementation proposal failed: " <> bridgeErrorMessage err)
                                         redirectTo ShowDecisionRecordAction { decisionRecordId }
                                     Right resp -> do
                                         newRecord @AgentProposal