Resume a session by pasting a session ID or resume command

[mcintyre94]

Stacked on #106 — merge that first.

Summary

• Session ID input in empty chat state — a new "Resume by session ID" field appears below session suggestions; accepts a bare UUID or a full claude --resume SESSION_ID ... command pasted directly from terminal output
• Automatic working directory discovery — looks up the session .jsonl file on the Sprite via find, reads .cwd from the file contents (more robust than decoding the directory name), and sets the working directory automatically before loading history
• Handles both bare UUIDs and full claude commands via UUID regex extraction
• Shows loading state while the Sprite wakes and the lookup runs; inline error if the session isn't found

Test plan

• Paste a bare session UUID → working directory is set correctly and history loads
• Paste a full claude --resume SESSION_ID "prompt" command → UUID is extracted and same flow runs
• Enter a non-existent session ID → inline error "Session not found on this Sprite"
• Enter something with no UUID → inline error "No valid session ID found"
• Works when Sprite is cold (wakes automatically during exec)

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