feat(zerocode): make terminal copy/paste work the way users expect

[JordanTheJet]

Summary

• Base branch: master
• What changed and why: In the zerocode TUI, mouse capture is enabled by default, which hijacks the terminal's own click-drag selection — so users could not select/copy text with the mouse — and Ctrl+V tried the clipboard image before text, adding a per-paste subprocess and surprising behavior on the common text path.
• Add a global selection mode toggle (Ctrl+O) that turns terminal mouse capture off/on at runtime. With it off, the terminal handles native drag-select, copy, and paste; a status-bar banner shows the mode and the exit key (read from the resolved keymap so a rebind stays accurate), and falls back to a compact form that leads with the exit key when the connection status crowds the column.
• Make Ctrl+V paste text-first, falling back to image attachment only when the clipboard holds no text — skipping the image-tool subprocess on the common path and complementing bracketed paste.
• Surface both affordances in the help modal: the selection-mode key and the Shift+drag native-selection hint most terminals support.
• Scope boundary: Does NOT change the OSC-52 copy path (y / Ctrl+Shift+C), bracketed-paste handling, or the startup mouse-capture default. No agent-switching changes (separate PR).
• Blast radius: Confined to apps/zerocode (TUI client): app event loop (app.rs), a new config_manager::set_mouse_capture terminal helper, the input-bar paste path, and one new GlobalAction. The toggle is loop-local state; capture state persists correctly across reconnect and is unconditionally disabled on exit by restore_terminal.
• Linked issue(s): None — addresses a direct user QOL request ("can't copy and paste easily").
• Labels: expect auto path/scope labels for apps/zerocode; suggest enhancement, size: S, risk: medium (touches apps/zerocode/src/**).

Validation Evidence (required)

cargo fmt --all -- --check
cargo clippy --all-targets -- -D warnings
cargo test

• Commands run and tail output:
  • cargo fmt --all -- --check → clean, no diff (exit 0).
  • cargo clippy --all-targets -- -D warnings → Finished with no warnings (exit 0).
  • cargo test → 0 failures across the workspace (grep -c "test result: FAILED" → 0). The zerocode package: test result: ok. 348 passed; 0 failed; 0 ignored and ok. 111 passed; 0 failed.
• Beyond CI — what did you manually verify? Traced the toggle through the event loop: Ctrl+O is a free global chord (no pane/input-bar binding), handled before pane dispatch and not gated on text-input, so it works from any pane and never reaches a pane handler. Confirmed the banner reads resolved_bindings() (rebind-accurate, matching the help modal) and compacts when left_area.width is below the full banner width. Verified text-first paste falls through to image attach when read_clipboard_text() returns None/empty (its documented contract), preserving the pure-screenshot workflow. NOT verified: behavior on every terminal emulator's Shift-drag override, and the both-flavors (text + image) clipboard case (documented tradeoff — text wins; attach images via /attach or Ctrl+A).
• If any command was intentionally skipped, why: None skipped.

Security & Privacy Impact (required)

• New permissions, capabilities, or file system access scope? No
• New external network calls? No
• Secrets / tokens / credentials handling changed? No
• PII, real identities, or personal data in diff, tests, fixtures, or docs? No
• If any Yes, describe the risk and mitigation: N/A. (Paste reads the local clipboard via the same already-present platform tools; no new capability.)

Compatibility (required)

• Backward compatible? Yes
• Config / env / CLI surface changed? Yes — adds a new rebindable keymap action global.toggle_mouse_capture (default Ctrl+O) and new info-bar/help strings. No migration; existing configs and keybinding overrides are unaffected, and Ctrl+O was previously unbound.
• If No or Yes to either: exact upgrade steps for existing users: None — additive and active by default. Note one intentional behavior change: Ctrl+V now prefers clipboard text over a clipboard image.

Rollback (required for risk: medium and risk: high)

Low blast radius (single TUI binary). git revert <sha> cleanly removes the toggle, the banner, the set_mouse_capture helper, and the text-first paste change; mouse capture reverts to always-on and Ctrl+V to image-first.