Pretty up login and sign up pages: Feature #173

[fairybladderwort]

Feature

Feature #173
Implements:

• Add scoped authentication form structure and semantic coverage #174
• Style and visually verify the responsive authentication experience #175

Prerequisite commit

• e67b4a12f901f76cc1214cacb8a100e2309cc14c — Development keys, retained in this PR at the user's direction.

Task commits

• 7436c82b783551b66f76cec8d30a42e2dc619bae — task Add scoped authentication form structure and semantic coverage #174: Add scoped authentication form structure and semantic coverage
• f4be818c06b62c842fa8bd56f6a7b7ef69552593 — task Style and visually verify the responsive authentication experience #175: Style and visually verify the responsive authentication experience

Validation

Task #174

• Focused authentication and route request suites: 10 examples, 0 failures.
• git diff --check passed.
• Independent implementation verification passed with no scope drift.
• Intent, security, naming, and performance review passed after replacing presentation-only section wrappers with neutral div elements.

Task #175

• Authentication-focused system, request, route, shared-header, and profile regression suites: 25 examples, 0 failures.
• Complete system suite plus focused request regressions: 48 examples, 0 failures.
• Authentication browser suite passed three consecutive focused repetitions after the final Turbo synchronization fix.
• Desktop and mobile visual verification covered login, sign-up, visible keyboard focus, validation feedback, responsive containment, and horizontal overflow at http://localhost:8000.
• git diff --check passed.
• Independent implementation verification passed with no scope drift.
• Intent, security, naming, and performance review passed after tightening focus, stylesheet-state, and vertical-reachability assertions.
• Final whole-PR intent, security, naming, and performance review passed after scoping responsive styles and isolating browser scenarios.
• User visual review approved the result.

[fairybladderwort]

Final whole-PR intent, security, naming, and performance review completed with no remaining findings. The retained development credential is encrypted, its key patterns remain ignored, authentication behavior and trust boundaries are unchanged, responsive styles are authentication-scoped, and the browser scenarios are isolated.