chore: drop non-code junk (pi-mono-reference, runtime state, root duplicates)

Remove files that should never have been tracked:

- pi-mono-reference/: 688-file copy of an upstream monorepo, zero imports,
  used only as offline human reference
- build/electron-builder.runtime.json: environment-specific build artifact
  with hardcoded local paths
- state/cancel-signal-state.json: runtime state written by the app
- prompt.txt, logo.svg (root): exact duplicates of the canonical copies
  under .planning/archive/ and assets/

Add state/ to .gitignore so future runtime state stays out.

pi-mono-reference/packages/coding-agent/examples/sdk/05-tools.ts

@@ -1,56 +0,0 @@
-/**
- * Tools Configuration
- *
- * Use built-in tool sets or individual tools.
- *
- * IMPORTANT: When using a custom `cwd`, you must use the tool factory functions
- * (createCodingTools, createReadOnlyTools, createReadTool, etc.) to ensure
- * tools resolve paths relative to your cwd, not process.cwd().
- *
- * For custom tools, see 06-extensions.ts - custom tools are now registered
- * via the extensions system using pi.registerTool().
- */
-
-import {
-	bashTool,
-	createAgentSession,
-	createBashTool,
-	createCodingTools,
-	createGrepTool,
-	createReadTool,
-	grepTool,
-	readOnlyTools,
-	readTool,
-	SessionManager,
-} from "@mariozechner/pi-coding-agent";
-
-// Read-only mode (no edit/write) - uses process.cwd()
-await createAgentSession({
-	tools: readOnlyTools,
-	sessionManager: SessionManager.inMemory(),
-});
-console.log("Read-only session created");
-
-// Custom tool selection - uses process.cwd()
-await createAgentSession({
-	tools: [readTool, bashTool, grepTool],
-	sessionManager: SessionManager.inMemory(),
-});
-console.log("Custom tools session created");
-
-// With custom cwd - MUST use factory functions!
-const customCwd = "/path/to/project";
-await createAgentSession({
-	cwd: customCwd,
-	tools: createCodingTools(customCwd), // Tools resolve paths relative to customCwd
-	sessionManager: SessionManager.inMemory(),
-});
-console.log("Custom cwd session created");
-
-// Or pick specific tools for custom cwd
-await createAgentSession({
-	cwd: customCwd,
-	tools: [createReadTool(customCwd), createBashTool(customCwd), createGrepTool(customCwd)],
-	sessionManager: SessionManager.inMemory(),
-});
-console.log("Specific tools with custom cwd session created");