feat: image paste (Ctrl+V) and drag-and-drop into terminal (#84)

* feat: add image paste and drag-and-drop support

Clipboard paste (Ctrl+V) and drag-and-drop of image files into the
terminal. Images are saved to {workdir}/.claude-images/ and the
absolute path is inserted into the terminal input for Claude to read.

- POST /api/sessions/:id/paste-image endpoint (hand-parsed multipart)
- image-input.js mixin with paste trap technique (works on HTTP)
- Ctrl+V intercepted at xterm keyboard level, routes through hidden
  contenteditable div to capture both image and text clipboard data
- Drag-and-drop on terminal container with visual overlay
- Session cleanup deletes .claude-images/ on destroy

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* security: remove SVG from paste-image allowlist

Drops .svg / image/svg+xml from the paste-image endpoint. SVGs are
served as image/svg+xml via /api/sessions/:id/file-raw, same-origin,
under a CSP that permits inline scripts — which would execute on view.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: arkon <arkon.85@hotmail.com>

src/web/server.ts

@@ -34,7 +34,7 @@ import fastifyStatic from '@fastify/static';
 import fastifyWebsocket from '@fastify/websocket';
 import { join, dirname } from 'node:path';
 import { fileURLToPath } from 'node:url';
-import { existsSync, mkdirSync, readFileSync, chmodSync } from 'node:fs';
+import { existsSync, mkdirSync, readFileSync, chmodSync, rmSync } from 'node:fs';
 import fs from 'node:fs/promises';
 import { execSync } from 'node:child_process';
 import { homedir, hostname as getHostname } from 'node:os';
@@ -943,6 +943,15 @@ export class WebServer extends EventEmitter {
       fileStreamManager.closeSessionStreams(sessionId);
       // Stop watching for images in this session's directory
       imageWatcher.unwatchSession(sessionId);
+      // Clean up pasted images directory for this session
+      if (killMux && session.workingDir) {
+        const pasteImageDir = join(session.workingDir, '.claude-images');
+        try {
+          rmSync(pasteImageDir, { recursive: true, force: true });
+        } catch {
+          // Best-effort cleanup
+        }
+      }
       await session.stop(killMux);
       this.sessions.delete(sessionId);
       // Only remove from state.json if we're also killing the mux session.