[Bugfix #252] Add image paste and mobile clipboard support to dashboard

[waleedkadous]

Summary

Fixes #252

• Adds image paste detection on Cmd+V (Mac) / Ctrl+Shift+V (Linux/Windows) using the Clipboard API
• Uploads image blobs to the existing /api/paste-image endpoint and pastes the resulting file path
• Adds a native paste event listener on the terminal container for mobile browser support (long-press paste menu)
• Shows upload progress indicator with error handling
• Falls back gracefully to text paste when clipboard.read() is unavailable

Root Cause

The existing paste handler only used navigator.clipboard.readText() which silently ignored image content in the clipboard. Mobile browsers couldn't trigger clipboard operations at all since they rely on native paste events rather than keyboard shortcuts.

Fix

1. Image detection: On paste, first tries navigator.clipboard.read() to check for image MIME types (png, jpeg, gif, webp, bmp)
2. Upload flow: When image detected, uploads blob via uploadPasteImage() (existing API), shows [Uploading image...] status, then pastes the file path
3. Mobile support: Registers a native paste event listener on the terminal container that handles both image and text paste from mobile context menus
4. Graceful fallback: If clipboard.read() is unavailable or denied, falls back to readText() for text paste

Test Plan

• Added 5 new regression tests (image paste via keyboard, fallback behavior, upload status, native paste event for mobile, text-only native paste)
• All 12 clipboard tests pass (7 existing + 5 new)
• Pre-existing StatusPanel test failures confirmed unrelated
• Net diff: 235 LOC (under 300 LOC BUGFIX threshold)

Acceptance Criteria

• Cmd+V with an image on the clipboard is handled (uploaded and path pasted)
• Shift+Enter inserts line continuation (was already implemented)
• Clipboard operations work on mobile browsers via native paste event listener

CMAP Review

Pending

[waleedkadous]

CMAP Review Summary

Gemini: REQUEST_CHANGES

• Flagged missing uploadPasteImage export (false positive — already exists in api.ts:157-169)
• Suggested extracting shared upload logic

Codex: REQUEST_CHANGES

• [Fixed] tryPasteImage leaves stale [Uploading image...] on upload failure
• [Fixed] No test for keyboard upload failure path
• [Fixed] MIME filtering inconsistency between keyboard and native paths

Claude: REQUEST_CHANGES

• Flagged missing uploadPasteImage (false positive — already in api.ts)
• [Fixed] Error handling inconsistency between keyboard and native paste paths
• [Fixed] No test for upload failure path
• Flagged Shift+Enter as new (false positive — already existed before this PR)

Changes Made (commit 4053cb2)

All legitimate issues addressed:

1. Added error handling in tryPasteImage for upload failures
2. Made MIME filtering consistent between both paths (IMAGE_TYPES allowlist)
3. Added regression test for keyboard upload failure path
4. Total: 13 tests passing (7 original + 6 new)

[waleedkadous]

CI Status

Unit Tests and Tower Integration Tests are failing — verified these are pre-existing failures on main (run #22016126192 on main shows identical failures):

• pty-session.test.ts: Flaky resume sequence test (same on main)
• Tower Integration Tests: bugfix-202, tower-api, tower-baseline all fail identically on main

Passing checks: CLI Tests (macOS + Ubuntu), CLI Integration Tests, Package Install Verification

No regressions introduced by this PR.