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/Widgets.hs

@@ -11,7 +11,7 @@ import IHP.ControllerPrelude
 import Data.Aeson (toJSON, object, (.=))
 import Application.Helper.Controller (isInRegression, widgetCycleCounts)
 import Application.Helper.TypeRegistry (validateWidgetType, validatePolicyScope, activeWidgetTypes, activePolicyScopes)
-import Application.Helper.AgentBridge (callAgent, checkGovernancePolicy)
+import Application.Helper.AgentBridge (callAgent, checkGovernancePolicy, bridgeErrorMessage)
 import Application.Helper.ModelRouter (resolveAgent)
 import Data.List (intercalate)
 
@@ -209,7 +209,7 @@ instance Controller WidgetsController where
                         result <- liftIO $ callAgent agent userMsg
                         case result of
                             Left err -> do
-                                setErrorMessage ("AI summarization failed: " <> err.errorMessage)
+                                setErrorMessage ("AI summarization failed: " <> bridgeErrorMessage err)
                                 redirectTo ShowWidgetAction { widgetId }
                             Right resp -> do
                                 newRecord @AgentProposal
@@ -258,7 +258,7 @@ instance Controller WidgetsController where
                         result <- liftIO $ callAgent agent userMsg
                         case result of
                             Left err -> do
-                                setErrorMessage ("AI draft failed: " <> err.errorMessage)
+                                setErrorMessage ("AI draft failed: " <> bridgeErrorMessage err)
                                 redirectTo ShowWidgetAction { widgetId }
                             Right resp -> do
                                 newRecord @AgentProposal