feat(ui): dynamic urgency color and per-cell report styling

[dianila68]

What

Adds cell-level style overrides on top of the existing row-wide taskwarrior color rules:

• table: new Row::CellStyledData variant carrying optional per-cell styles, patched over the row style (and over the highlight style when the row is selected), so an override that only sets a foreground keeps the row background.
• report_style (new module): the urgency column is colored on a green → yellow → red gradient, scaled proportionally to the most urgent visible task and saturating at a configurable cap so a single outlier cannot compress the scale. Columns adjacent to the description can get a distinct tint.
• task_report: simplify_table now records visible_columns, so display indices can be mapped back to taskwarrior column names after empty columns are dropped.

Configuration

uda.taskwarrior-tui.urgency.dynamic-color=true   # default: true
uda.taskwarrior-tui.urgency.color-cap=15         # default: 15
uda.taskwarrior-tui.style.report.near-description=   # default: empty (no tint)

Notes

• Related to the per-column coloring discussion in the issue tracker (task color based on column value).
• Unit tests included for the gradient, cap behavior and neighbor tinting.
• cargo fmt, cargo clippy -- -D warnings clean.

🤖 Generated with Claude Code