feat(terminal): Mouse Mode Submit button for agent terminal panes (#819)

[Juliusolsson05]

Closes #819.

What

Adds a Mouse Mode-gated Submit row so a mouse-only user can press Enter inside an agent terminal pane (AgentTerminalLeaf) after dictating or pasting a command into the raw PTY. Clicking Submit routes the Enter byte ('\r') through the existing keypress pipeline (terminalInputForwarder + the pre-attach pendingInput queue), so a mouse click and a real Enter are byte-identical to the backend — no read/clear of any draft (terminal view has none by design), no new setting (reuses mouseModeEnabled), zero layout change when off.

Scope

• AgentTerminalLeaf only. Added: src/renderer/src/workspace/tile-tree/AgentTerminalActions.tsx (+ colocated test) and wiring in AgentTerminalLeaf.tsx (selector, a ref the mount effect publishes the routing closure on, and the gated row).
• TerminalLeaf (plain shells) and ComposerActions are byte-identical — confirmed via git diff against main.
• Stop button deliberately out of scope (deferred follow-up — interrupt semantics differ per TUI).

Design/plan

• docs/superpowers/specs/2026-09-05-mouse-mode-terminal-submit-design.md
• docs/superpowers/plans/2026-09-05-mouse-mode-terminal-submit.md

Verification (Node v24.14.1, matching .nvmrc/CI)

• npm run typecheck (control-sdk + tsc -b): exit 0
• npm run test:renderer: 123 files / 522 tests passing (baseline 121/514, +2 files/+8 tests)
• node scripts/verify-submodule-checkouts.mjs: verified

Tests added

• AgentTerminalActions.renderer.test.tsx (5): renders one always-enabled button, mousedown preventDefault (xterm focus preserved) + still bubbles (leaf engagement), click fires onSubmit, composer scaffold classes.
• AgentTerminalLeaf.submit.renderer.test.tsx (3): button hidden when mouse mode off; sends '\r' to the PTY after attach when on; queues a pre-attach Submit and delivers it on attach.

Note for maintainers/reviewers: this repo's renderer suite requires Node 24. Node 25 (this machine's default) breaks happy-dom's localStorage with 34 spurious storage.setItem is not a function failures.

Do not merge — awaiting explicit maintainer confirmation.

[Juliusolsson05]

Read the full diff against the mouse-first workspace plan and #819's acceptance criteria.

• Submit routes '\r' through the same forwarder + pre-attach queue the keyboard uses, so a click before attach is queued and a click during replay is dropped exactly like a keypress. The closure reads forwarder.replaying and attachedBackfillDone at call time, so no stale capture.
• TerminalLeaf.tsx and ComposerActions.tsx are byte-identical to main (checked with git diff origin/main...HEAD).
• Merged current main (23 commits) into the branch: no conflicts; npm run typecheck clean; the two new test files pass on Node 24 (8 tests).
• One observation, not a blocker: the leaf test detects the Node 25 happy-dom problem only in the PR body. .nvmrc already pins 24, so nothing to change.

Approve. Waiting for the maintainer's merge confirmation per repository policy.