Simplify color detection

[kevinmcconnell]

When detecting terminal colors at startup:

• Ensure we consume the sentinel marker, so as not to leak it back to the terminal on exit
• Simplify the logic for processing the response: we can just read and parse the incoming buffer until we get the sentinel, and close the reader on timeout

[Copilot]

Pull request overview

This PR refactors terminal palette detection to read/parse escape sequences incrementally until the DA1 “sentinel” is received (or a timeout closes the TTY), reducing buffering/coordination complexity and ensuring the sentinel response is consumed before exiting.

Changes:

• Replaced channel/goroutine-based buffering with a detector that reads OSC/CSI sequences directly from a bufio.Reader.
• Updated detection flow to always wait for the DA1 sentinel (or stop on read error) and to close the TTY on timeout via a single cleanup path.
• Reworked tests to validate the new incremental reader behavior and the updated detectFrom signature.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
internal/ui/palette_detect.go	Implements the new incremental detector (OSC/CSI parsing), and changes timeout handling to close/restore the TTY via a single cleanup function.
internal/ui/palette_detect_test.go	Updates tests to exercise readNext/detector behavior and adjusts detectFrom call sites for the new API.

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