feat(statusline): cost-tier colors for model/effort + output-style segment

[johnsje183]

What

Two additions that make the left edge of the line more informative:

1. Cost-tier colors for the model family and effort code. Both scale green (cheap) → bold red (most expensive): Ha green, So yellow, Op orange, Fb/My bold red; lo → md → hg → xhg → mx on the same scale. The context bar and rate-limit percentages already communicate urgency by color — this extends the idea to "how expensive is this session", readable at a glance without parsing text. The context-size suffix stays in its own dim span; unknown families and unknown effort levels keep the previous all-dim rendering, so unrecognised models are visually unchanged.

2. style:expl output-style segment. Claude Code reports the active output style on stdin (output_style.name). A non-default style (Explanatory, Learning, or a custom one) changes how the assistant responds, is stored per settings scope — so it quietly differs between projects — and is easy to switch on and forget. Rendered as a dim label + magenta value right after the model segment. Known styles get readable short codes (expl, learn); unknown styles abbreviate to their first five chars. The default style renders nothing.

House rules

• No deps, single file, exit-0-on-error preserved (the style segment is wrapped in its own try/catch)
• Hide on happy path: default style is invisible, existing setups without styles render byte-for-byte the same line text
• Only widely-supported ANSI codes: 30–37, 1;31, and the truecolor orange already used elsewhere — no TUI-incompatible attributes
• Own-key lookups on all new maps (FAMILY_COLORS, EFFORT_COLORS, KNOWN_STYLES), matching the EFFORT_CODES prototype guard from feat(statusline): show reasoning-effort tier as a 2-letter code after the model #6

Testing

node tests/statusline-smoke.test.js — green. The effort raw-span assertion is updated for the new colors, plus three new cases: family cost-tier colors (incl. dim fallback for unknown families), dim fallback for unknown effort levels, and output-style visibility rules (known / custom / default / absent). The README segment table is updated for both features.

Example (Fable 5, xhigh effort, Explanatory style):

Fb5:xhg (1m) │ style:expl │ myproject (main) │ ██░░░ 250k/1M │ ...

with Fb5 bold red, :xhg red, (1m) dim, expl magenta.

🤖 Generated with Claude Code