Add formatted JSON modes to the expanded reader

[robince]

Summary

• add reader content modes so expanded cells can switch between raw text and pretty-printed JSON
• default JSON-looking string values to a formatted, syntax-colored reader view with a mode badge and F toggle
• preserve existing reader navigation while falling back to raw mode when a new row does not support JSON formatting

Testing

• go test ./internal/ui
• go test ./...

[Copilot]

Pull request overview

Adds multi-format rendering to the expanded cell reader, enabling automatic pretty-printed + syntax-colored JSON viewing (with a mode badge and F toggle) while preserving existing reader navigation and falling back to raw when formatting isn’t available.

Changes:

• Introduces reader modes (raw, json pretty) with mode cycling (F) and automatic JSON-pretty defaulting for JSON-looking values.
• Adds JSON pretty-printing + lightweight syntax highlighting, plus ANSI-aware wrapping/slicing for reader rendering.
• Updates reader UI (header badge, footer/bottom-bar hints) and extends tests for mode selection, toggling, and fallback behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
internal/ui/styles.go	Adds lipgloss styles for reader mode badges and JSON syntax token colors.
internal/ui/reader_render.go	Implements reader mode logic, JSON pretty formatting, syntax highlighting, and ANSI-aware wrapping/slicing helpers.
internal/ui/model.go	Stores reader mode state in the model, wires mode refresh/fallback on row changes, adds F handler, and updates reader rendering to use the new renderer.
internal/ui/model_test.go	Adds/updates tests covering default JSON mode selection, invalid JSON behavior, F toggling, row-navigation fallback, and badge/rendered output checks.

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[robince]

@codex review

[chatgpt-codex-connector]

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