Move exec to HookAPI, sessionManager/modelRegistry to HookEventContext

Breaking changes:
- HookEventContext now has sessionManager and modelRegistry (moved from SessionEventBase)
- HookAPI now has exec() method (moved from HookEventContext/HookCommandContext)
- HookRunner constructor takes sessionManager and modelRegistry as required params
- Session events no longer include sessionManager/modelRegistry fields

Hook code migration:
- event.sessionManager -> ctx.sessionManager
- event.modelRegistry -> ctx.modelRegistry
- ctx.exec() -> pi.exec()

Updated:
- src/core/hooks/types.ts - type changes
- src/core/hooks/runner.ts - constructor, createContext
- src/core/hooks/loader.ts - add exec to HookAPI
- src/core/sdk.ts - pass sessionManager/modelRegistry to HookRunner
- src/core/agent-session.ts - remove sessionManager/modelRegistry from events
- src/modes/* - remove setSessionFile calls, update events
- examples/hooks/* - update to new API

packages/coding-agent/examples/hooks/dirty-repo-guard.ts

@@ -15,7 +15,7 @@ export default function (pi: HookAPI) {
 		}
 
 		// Check for uncommitted changes
-		const { stdout, code } = await ctx.exec("git", ["status", "--porcelain"]);
+		const { stdout, code } = await pi.exec("git", ["status", "--porcelain"]);
 
 		if (code !== 0) {
 			// Not a git repo, allow the action