Keep self-upgrade progress interruptible

[kindermax]

Summary

Follow up on #425 to fix the remaining Ctrl-C failure while lets self upgrade is displaying download progress.

• Use the existing throttled carriage-return renderer for interactive downloads instead of starting a Bubble Tea program.
• Add regression coverage that rejects terminal keyboard-mode control sequences in progress output.
• Clarify the Unreleased changelog entry with the actual behavior being fixed.

Root Cause

The Bubble Tea renderer enabled modifyOtherKeys and Kitty keyboard mode even though progress input was disabled. Supporting terminals then encoded Ctrl-C as a key event instead of generating SIGINT; the progress program ignored that input, so the CLI context was never canceled and the download continued.

The signal cleanup added in #425 remains useful, but it could not receive a signal while the progress renderer had changed terminal keyboard handling.

User Impact

Ctrl-C now remains a normal terminal interrupt during self-upgrade downloads, allowing the shared CLI context to cancel the HTTP request and extraction promptly. Other download progress indicators use the same terminal-safe renderer.

Validation

• Deterministic PTY reproduction: before the fix, encoded Ctrl-C was ignored and progress reached 100%; after the fix, no keyboard modes are enabled and Ctrl-C terminates immediately.
• go test ./internal/progressbar ./internal/cli ./internal/upgrade/registry
• go test ./...
• lets lint
• lets test-bats (150 tests)

Summary by Sourcery

Simplify download progress rendering to avoid terminal keyboard mode changes that interfere with Ctrl-C interrupts during self-upgrade.

Bug Fixes:

• Ensure self-upgrade download progress does not intercept Ctrl-C so terminal interrupts cancel the operation as expected.

Enhancements:

• Use the throttled, non-interactive progress renderer consistently instead of the Bubble Tea-based animated progress bar.
• Update terminal width detection to rely directly on the shared terminal writer utility.

Build:

• Adjust module dependencies to treat Bubble Tea as an indirect dependency and mark golang.org/x/sys as a direct dependency.

Documentation:

• Clarify the changelog entry to describe that self-upgrade progress indicators no longer intercept Ctrl-C.

Tests:

• Add regression coverage asserting that progress output does not emit terminal keyboard-mode control sequences.
• Remove obsolete tests tied to the Bubble Tea-based progress model.

[sourcery-ai]

Reviewer's Guide

Ensure self-upgrade and other download progress indicators always use the existing throttled carriage-return renderer, removing Bubble Tea-based animation so Ctrl-C remains a normal terminal interrupt and adding regression tests and docs updates around terminal-safe behavior.

File-Level Changes

Change	Details	Files
Simplify the progress observer to always use the manual, throttled carriage-return renderer instead of running an animated Bubble Tea program.	Remove animation-related fields and options from the Observer (animate, finalPause, WithFinalPause) and default to non-animated rendering Delete animatedTracker and progressModel implementations that used Bubble Tea to drive progress animation and window size handling Retain manualTracker-based progress updates with throttling for both known-size and unknown-size downloads	internal/progressbar/progress.go
Harden progress output against terminal keyboard-mode side effects and add regression coverage.	Add a test ensuring Observer output for self-update downloads does not contain modifyOtherKeys or Kitty keyboard mode escape sequences Update existing Observer tests to reflect removal of WithFinalPause and animation-only behavior Remove obsolete tests that exercised Bubble Tea-based progressModel logic	internal/progressbar/progress_test.go
Adjust terminal detection utility usage to centralize terminal handling behavior.	Simplify detectWidth to use util.IsTerminalWriter directly instead of a local isTerminal helper Remove the redundant isTerminal wrapper function	internal/progressbar/progress.go
Update module dependencies to reflect removal of direct Bubble Tea usage and promotion of x/sys to a direct dependency.	Remove charm.land/bubbletea/v2 from the main require block and keep it only as an indirect dependency Change golang.org/x/sys from an indirect to a direct dependency	go.mod
Clarify documentation of the fixed behavior around Ctrl-C during self-upgrade.	Update the Unreleased changelog entry to describe that download progress indicators no longer intercept Ctrl-C during lets self upgrade	docs/docs/changelog.md

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