Redesign Highlands theme — strengthen warm moorland dark identity

[gregpriday]

Summary

The Highlands theme is a warm dark theme with brown-grey surfaces inspired by Scottish moorland. It reads as pleasant but somewhat anonymous — it lacks the distinctiveness of Daintree or Arashiyama. The terminal palette is muted to the point of reduced legibility, and the theme doesn't yet fully express the highlands character: heather purple, pewter sky, peaty shadow.

Problem Statement

Highlands uses surfaces #1A1614 (canvas) and #14110F (sidebar) — a warm charcoal brown. The feel is correct in direction but unfinished:

• The warmth is subtle to the point of being unnoticeable. At small sizes or quick glances, Highlands looks nearly identical to a generic dark grey theme.
• Terminal colors are intentionally desaturated (the muted palette approach works for Arashiyama and Galápagos), but terminal-green: #4E8C6A and terminal-blue: #5B7E96 are dark enough to risk legibility issues on the canvas background. terminal-magenta: #8B6A8A in particular is very dim.
• syntax-string: #C88C45 is a warm amber that's used as the primary syntax color, but this competes with syntax-number: #BE7055 which is also a warm tone — they're hard to differentiate at a glance.
• The theme has no strong secondary hue that gives it character. Daintree has its cool grey neutrality, Arashiyama has its warm bamboo amber/rust. Highlands needs something — heather purple, moss green, or pewter blue — to anchor its identity.
• activity-idle: #4A4238 is very close to the surface-canvas value, making idle worktrees barely distinguishable from the background.

Relevant code:

• shared/theme/themes.ts#L388-L450 — current Highlands token definitions

Desired Behavior

Highlands should feel like the Scottish moorlands: warm dark earthy tones with heather purple accents, grey-pewter sky mid-tones, and deep peat-brown surfaces. The theme should:

• Have a clear identity hue (heather purple or pewter blue) worked into syntax highlighting and/or activity indicators.
• Terminal colors should be legible — all normal ANSI colors should achieve contrast ≥ 3:1 on the canvas background.
• syntax-string and syntax-number should be differentiable — distinct enough hues that code doesn't look monochrome.
• activity-idle should be visually distinct from the canvas surface.

Verification Workflow

1. Apply the theme: await setAppTheme(window, "highlands").
2. Capture full-page screenshot.
3. Measure terminal color contrast against canvas for each ANSI color.
4. AI visual evaluation: does the theme have a clear highlands character? Are the syntax colors distinguishable? Does it look distinct from Daintree?
5. Iterate and npm run check.

Acceptance Criteria

• The theme has a recognizable secondary identity hue beyond warm-brown surfaces (heather, pewter, or similar moorland-inspired tone).
• All standard ANSI terminal colors meet ≥ 3:1 contrast against surface-canvas.
• syntax-string and syntax-number are visually distinct from each other.
• activity-idle is clearly visible against the canvas — it should read as a meaningful UI signal, not blend in.
• All E2E tests pass.

Edge Cases & Risks

• Terminal scheme pairing from PR feat(terminal): match terminal color scheme to app theme automatically #3345 — verify app/terminal visual cohesion after token changes.
• Highlands category colors currently use the default shared dark-theme oklch values; if the theme redesign introduces a strong secondary hue, the category colors should be evaluated for coherence.

[gregpriday]

Terminal color scheme — review as part of redesign

The APP_THEME_TERMINAL_SCHEME_MAP currently maps highlands → canopy-ember (Canopy Ember). As part of this theme redesign, review whether the terminal color scheme still pairs well with the updated app surfaces:

1. Evaluate the current pairing — after updating the surface/accent tokens, check whether Canopy Ember still feels cohesive. If the surface palette shifts significantly, the terminal may look disconnected.
2. Research alternatives — search for well-known open-source terminal color schemes whose character matches the redesigned theme. Evaluate candidates for ANSI color legibility against the new surface background, not just aesthetic similarity.
3. Consider a bespoke scheme — if no existing scheme is a tight fit, create a dedicated one derived from the redesigned app tokens (like we did for Daintree via getTerminalThemeFromAppScheme). This gives the tightest visual integration.
4. Adapt rather than copy — if borrowing an open-source palette, adjust selection background, cursor, and bright variants so they harmonize with the app's surface/accent tokens.

Update APP_THEME_TERMINAL_SCHEME_MAP in src/config/terminalColorSchemes.ts and add any new scheme to the BUILT_IN_SCHEMES array. Update the test count in src/config/__tests__/terminalColorSchemes.test.ts if adding a new scheme.