Add ANSI SGR-encoded screen output to screenshot (#22)

* Add ANSI SGR-encoded screen output to screenshot

The screenshot response now includes a `screen_ansi` field containing the
screen content with inline ANSI SGR escape sequences, preserving colors
and text attributes (bold, italic, underline, blink, reverse). This makes
TUI app screenshots readable by agents that understand ANSI codes.

- Add `no_color` field to ScreenshotRequest, `screen_ansi` to ScreenshotResponse
- Build ANSI string in Emulator.Screen() with delta-encoded SGR sequences
- Support standard ANSI (0-15), 256-color palette (16-255), and 24-bit RGB
- Wire through daemon handler, CLI --no-color flag, and plain text output
- Add 7 integration tests covering colors, attributes, no-color, and pipeline

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Fix review issues: pipeline NoColor, trailing styled spaces, buildSGR correctness

- Thread NoColor from ScreenshotRequest through pipeline ScreenshotStep
- Preserve trailing styled spaces in screen_ansi with two-pass column scan
- Don't re-emit SGR 7 (reverse) — vt10x already materializes it by swapping FG/BG
- Use isDefaultColor(c >= DefaultFG) to catch all sentinel values including swapped defaults
- Add 12 unit tests for buildSGR, fgSGR/bgSGR, isDefaultColor/Style, trailing spaces
- Add integration test for pipeline screenshot with no_color=true

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Update SKILL.md with screen_ansi docs and --no-color flag

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Fix lint: errcheck on Close, staticcheck SA5011 nil guard

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Refocus emulator tests on screen behavior

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Fix errcheck lint: discard conn.Close error in waitForReady (#17)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Add Homebrew tap to goreleaser and install instructions to README (#3)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Add goreleaser with GitHub Actions release on tag push (#2)

- .goreleaser.yml: linux/darwin amd64+arm64, CGO_ENABLED=0, ldflags for version info
- .github/workflows/release.yml: triggers on v* tags
- cmd/virtui: add version command with --json support

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>