More color customization

[ChronoInferna]

Problem Statement
ticker currently limits user customization to a small subset of UI color elements (text, text-light, text-label, text-line, text-tag, background-tag). However, important interface components—such as the bottom summary/status bar, change indicators, borders, and inactive elements—inherit hard-coded ANSI colors. This restricts integration with themed environments (e.g., Rosé Pine, Gruvbox, Solarized) and prevents full visual coherence when used in color-managed terminals or themed dashboards.

Proposed Solution
Extend the colors configuration struct in config/config.go to include new optional keys for additional UI regions and semantic roles, for example:

colors:
  summary-text: "#e0def4"
  summary-background: "#26233a"
  gain: "#9ccfd8"
  loss: "#eb6f92"
  border: "#403d52"
  highlight: "#f6c177"

These would be accessed in ui/view.go (and other renderers) via the existing config.Colors object, with sensible fallbacks to current ANSI defaults when unspecified. This maintains backward compatibility while enabling full theme customization through YAML.

Alternatives

1. Relying on terminal color tables or ANSI overrides (works partially but not portable).
2. Using wrappers like grc or colout to post-process output (inefficient and brittle).
3. Forking ticker and editing view.go directly (not maintainable for most users).

Use Cases

• Users applying consistent theming across CLI tools (Rosé Pine, Catppuccin, Gruvbox, etc.).
• Integrations with dashboards or status bars where color control must match existing palettes.
• Accessibility adjustments (high contrast, colorblind-friendly schemes).

Additional Context
Example YAML configuration using Rosé Pine palette:

colors:
  text: "#e0def4"
  text-light: "#f6c177"
  text-label: "#9ccfd8"
  text-line: "#c4a7e7"
  text-tag: "#31748f"
  background-tag: "#26233a"
  summary-background: "#1f1d2e"
  summary-text: "#e0def4"
  gain: "#9ccfd8"
  loss: "#eb6f92"

This change would allow full visual parity between ticker and modern CLI ecosystems that emphasize theme consistency.