refactor(messaging): project inter-agent messages into pi session transcript

Inter-agent messages previously entered the recipient's context as a
separate prompt block (recentMessages), rebuilt every turn. This double-
charged tokens and kept messages outside pi's native AgentMessage stream.

Now at prepareRun: pull the recipient's unread inbox, project each
AgentMessageRecord into a pi user-role AgentMessage, persist to
SqliteSessionStore, and mark delivered. The recipient reads messages
as natural conversation turns in the transcript.

- db: listAgentInboxUnread + markAgentInboxDelivered (transactional)
- agent-runtime/inbox-projection.ts: AgentMessageRecord -> pi AgentMessage
- runtime-bridge.prepareRun: inject + deliver before loadMessages
- prompt-builder: delete recentMessages context block + buildMessagesSection
- message-normalize: drop unused normalizeMessagesForPrompt
- delete prompt-builder/attachment-resolver.ts (orphan after section removal)

Send path (api-server/routes-messages, ipc, UI) unchanged — inbox table
remains the UI source. Transactional delivery marking prevents duplicate
injection across runs. Failed append -> no mark -> retry on next run.

src/main/prompt-builder/index.ts

@@ -1,4 +1,4 @@
-import type { AgentRecord, AgentMessageRecord, ApprovalRecord, DocumentRecord, ExecutionMode, GoalRecord, KnowledgeEntryRecord, MeetingRecord, ProjectRecord, SprintRecord, TaskRecord } from "@shared/types";
+import type { AgentRecord, ApprovalRecord, DocumentRecord, ExecutionMode, GoalRecord, KnowledgeEntryRecord, MeetingRecord, ProjectRecord, SprintRecord, TaskRecord } from "@shared/types";
 import type { AppLocale } from "@shared/locale";
 import type { ProjectedSkill } from "../skill-types";
 import { buildSystemPrompt } from "./system-prompt";
@@ -28,7 +28,6 @@ export interface PromptContext {
   recentComments: Array<{ taskId: string; taskTitle: string; authorName: string; body: string; createdAt: string }>;
   companyDescription: string;
   socialAccounts: Array<{ id: string; platform: string; accountName: string; status: string; requireApproval: boolean }>;
-  recentMessages?: AgentMessageRecord[];
   upcomingMeetings?: MeetingRecord[];
   relevantKnowledge?: KnowledgeEntryRecord[];
   activeSprint?: SprintRecord | null;