feat(theme)!: standardize theme scopes and remove legacy APIs

[leoafarias]

Description

Add theme, darkTheme, and mode to FortalScope and both generated preset scopes. Root scopes supply light/dark defaults and follow live system brightness. A supplied theme without darkTheme is used in both modes; nested scopes inherit the configured pair and current selection. The application owns the mode preference.

Use WidgetsApp throughout the dashboard, examples, generated-consumer hosts, documentation, skills, and downloadable tutorials. Put routed scopes in the app builder above the Navigator. Preserve application-owned custom tokens. The scope supplies appearance; no new app wrapper is introduced.

Enforce the hard cutoff with a lexical guard that handles comments, strings, named constructors, typed declarations, configured prefixes, and tutorial/integration tests while allowing unrelated scope APIs. Regression tests assert inherited token colors, custom-theme preservation, live dialogs, and text-style inheritance across host placements.

Related Issues

Stacked on #211. Merge #211 first, then retarget this PR to main.

Validation

Current follow-up commit:

• Fresh CLI consumers analyze and pass: default 376 tests; Fortal 13 tests.
• Fortal package: 822 tests; dashboard: 95 tests; demo: 61 tests.
• Downloadable tutorials: default 13 tests; Fortal 14 tests.
• Guard: 8 regression tests and the full repository/archive scan pass.
• Documentation validator: 148 analyzable Dart examples pass.
• Fortal template parity and both checked-in consumers pass; the declared token customization remains intact.
• Canonical theme-test static analysis passes.
• Current-head CI passed: full workspace tests, Windows CLI, icon checks, production docs/catalog/dashboard build, exported routes/assets, and static search.

The prior dashboard browser verification covered light/dark/system selection, charts, tables, dialog open/Escape, and no console errors. This follow-up changes test hosts and guidance without changing application runtime behavior. Original tutorial screenshots predate the host/theme migration; the archive contains updated tested source.

Checklist

• Includes tests for changed behavior and enforcement.
• Updates relevant documentation and skills.
• Follow up on review comments.

Breaking Change

• Yes, this is a breaking change.
• No, this is not a breaking change.

Remove default-scope data, FortalScope brightness, and configuration createScope APIs without aliases. Use theme for supplied values and mode for appearance selection. Theme data/configuration retains resolved brightness; intentional direct Fortal design options remain available. Migrate installed source and callers together.