fix(coding-agent): guard pasted shell prompts from python

[roboomp]

Repro

A pasted terminal transcript beginning with a shell prompt, e.g. $ cd ~/project && sudo ./build-and-push.sh o5.7 2>&1 | tail -4 followed by OMP status-line chrome, was submitted through the direct Python shortcut path. The focused regression command bun test packages/coding-agent/test/input-controller-python-prefix.test.ts failed before the fix because handlePythonCommand was called once for the pasted transcript.

Cause

packages/coding-agent/src/modes/controllers/input-controller.ts treated any trimmed input beginning with $ as a Python shortcut. That prefix collides with copied shell-prompt transcripts from terminals, so pasted UI text starting with $ cd ... was stripped to cd ... and sent to handlePythonCommand, producing Python SyntaxError output instead of a normal prompt.

Fix

• Added shell-prompt transcript detection before the single-$ Python shortcut route.
• Kept $$ ... and ordinary $ print(1) Python shortcuts working.
• Added regression coverage in packages/coding-agent/test/input-controller-python-prefix.test.ts for the reporter’s $ cd ... plus OMP status-line paste shape.
• Added an Unreleased changelog entry for packages/coding-agent.

Verification

Reproduced with bun test packages/coding-agent/test/input-controller-python-prefix.test.ts before the parser guard: 3 pass, 1 fail, with handlePythonCommand called for the pasted transcript. After the fix, bun test packages/coding-agent/test/input-controller-python-prefix.test.ts passes: 4 pass, 0 fail, 12 assertions. gh_push_branch completed the pre-publish gate and pushed farm/f1201b98/syntax-paste-python-exec. Fixes #4678

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