fix(tui): treat absolute file paths as plain text, not commands

[Tibsfox]

TL;DR

What: Dragging a file into Pi no longer triggers "Unknown command" errors.
Why: Absolute paths like /Users/name/file.png were parsed as /Users slash command.
How: Detect file paths (contain / after position 0) and bypass slash command dispatch.

What

When a file is dragged into the Pi TUI input field, the absolute path (e.g., /Users/name/Desktop/screenshot.png) starts with / and is interpreted as a slash command. This shows Error: Unknown command: /Users/name/Desktop/screenshot.png.

The fix adds a looksLikeFilePath() heuristic before the slash command check: if the first token contains a / after position 0 (like /Users/name/...), it's a file path, not a command. Slash commands are single tokens like /help or /gsd — they never contain embedded slashes.

Why

• Drag-and-drop is a common workflow, especially for screenshots (File drag-and-drop into Pi TUI is interpreted as a slash command #3478)
• The error is confusing — users don't expect file paths to be parsed as commands
• This worked in GSD v1 (Claude Code) — regression in Pi

How

• input-controller.ts: Added looksLikeFilePath() guard before text.startsWith("/") command dispatch
• Heuristic: first whitespace-delimited token has / at position >0 → file path, not command
• File path text falls through to session.prompt() as normal user input

Change type

• fix

Test plan

• /Users/name/Desktop/screenshot.png sent as plain input (new test)
• /home/user/documents/file.txt sent as plain input (new test)
• /tmp/some-file.log sent as plain input (new test)
• /settings still dispatched as slash command (existing test)
• /gsd help still dispatched as slash command (existing test)
• Unknown commands still show error (existing test)
• All 10 tests pass (7 existing + 3 new)

Closes #3478

🤖 Generated with Claude Code

[github-actions]

🟠 PR Risk Report — HIGH

Files changed	2
Systems affected	2
Overall risk	🟠 HIGH

Affected Systems

Risk	System
🟠 high	Modes
🟡 medium	TUI Components

File Breakdown

Risk	File	Systems
🟠	packages/pi-coding-agent/src/modes/interactive/controllers/input-controller.ts	Modes, TUI Components
⚪	packages/pi-coding-agent/src/modes/interactive/controllers/input-controller.test.ts	(unclassified)

⚠️ High risk — please run full integration tests and verify tool/extension contracts.

[allcounter]

Nice