Silence render-disposed spam, unbreak bundled skills, drop board wake

Three independently ugly bugs that all fed the same log flood:

* Electron's `WebFrameMain.send` writes every "Render frame was disposed"
  to stderr via `console.error`. When the worker fans a second
  agent-event past a reloading renderer, we produced thousands of
  identical lines and stalled the main loop on stderr I/O. Added a
  `mainFrame.detached` guard so the send is short-circuited before
  Electron's own catch block fires, and installed a targeted filter in
  `suppress-warnings.ts` (now actually imported from the entry point)
  so the specific `console.error("Error sending from webFrameMain:"…)`
  noise never reaches the terminal. Any other payload still surfaces.

* `dispatchAgentMessage` accepted the human-reader sentinel as a wake
  target when an agent replied to `__board__` — `wakeAgentIfPossible`
  then called `db.getAgent("__board__")`, threw, and the dispatcher
  kept repeating on every send. Strip `HUMAN_SENDER_ID` at
  `resolveMessageWakeTargets`, and keep a defense-in-depth guard in the
  heartbeat so a stray caller (future automation fan-out) cannot
  reintroduce the crash.

* Pi's skills loader rejects any SKILL.md whose frontmatter `name`
  diverges from its parent directory. The four bundled `my-writing-style`
  copies declared `name: writing-style-skill`, so every install emitted
  a warning and dropped the skill. They also lived as orphan gitlinks
  (mode 160000 without .gitmodules), and the global `*.md` gitignore
  hid every other SKILL.md from version control. Fixed the frontmatter
  to match the dir, converted the dangling submodules to plain trees,
  and allowlisted `builtin-skills/**/*.md` so a fresh clone carries the
  catalogue instead of silently losing it.

src/main/orchestration/heartbeat.ts

@@ -4,6 +4,7 @@ import type { AgentRecord, ConnectorRecord } from "@shared/types";
 import type { OrchestrationDependencies } from "./types";
 import type { RunDispatchParams } from "./turn-context";
 import { pickModelForAgent } from "../model-dispatch";
+import { HUMAN_SENDER_ID } from "../message-dispatch";
 
 /**
  * Every reason a heartbeat attempt can be rejected before a run is
@@ -258,6 +259,12 @@ export function createHeartbeat(
 
   function wakeAgentIfPossible(agentId: string | null | undefined, companyId: string, trigger: string, context?: Record<string, unknown>) {
     if (!agentId || isQuitting()) return null;
+    // `__board__` is the human participant sentinel, not an agent row.
+    // Upstream filters should strip it before we get here, but keeping
+    // this guard as defense-in-depth prevents a single stray call site
+    // (e.g. a future automation action that forwards the `toAgentId`
+    // raw) from spamming the log with "Agent not found: __board__".
+    if (agentId === HUMAN_SENDER_ID) return null;
     try {
       const agent = db.getAgent(agentId);
       if (agent.companyId !== companyId) {