## Why

Several regressions and UX defects slipped in after recent enhancements, affecting modal behavior, sharing visibility, footer/header usability, and image relevance. Fixing these together will restore trust, readability, and navigation quality without introducing new product scope.

## What Changes

- Fix permalink-to-hero modal behavior so image rendering and keyboard close (`Escape`) work consistently.
- Restore footer contact email visibility and ensure env-driven contact link rendering is reliable.
- Fix light-theme contrast for social share icons and add a copy-to-clipboard action alongside X, WhatsApp, and LinkedIn.
- Replace inline footer "Back to Top" text button with a floating island-style control.
- Make footer persistently sticky and compact while preserving reading comfort.
- Make header persistently sticky with subtle shrink, elevation, and glass effect on scroll.
- Tighten article-image relevance to avoid clearly unrelated images for finance/market stories.
- Remove unnecessary per-card "Link" affordance from feed cards.

## Capabilities

### New Capabilities
- None.

### Modified Capabilities
- `article-permalinks-and-deep-link-modal`: Correct deep-link modal open-state parity for hero/feed targets and keyboard close behavior.
- `share-and-contact-microinteractions`: Fix share-icon visibility in light mode, add copy-link action, and restore contact-email presence.
- `footer-policy-links`: Update footer interaction model for sticky compact layout and floating back-to-top control.
- `responsive-device-agnostic-layout`: Apply sticky header/footer behavior and ensure readability is not degraded.
- `news-image-relevance-and-fallbacks`: Improve relevance guardrails to reduce obviously mismatched fallback/provider image outcomes.
- `hero-display`: Remove redundant card-level permalink text affordance where it harms clarity.

## Impact

- **Frontend UI:** `frontend/index.html` modal behaviors, keyboard handling, share controls, footer/header interactions, and card affordances.
- **Backend config/data:** contact link exposure verification through `/config` payload and env handling.
- **Image pipeline:** backend relevance and fallback heuristics in image selection paths.
- **UX quality:** stronger consistency across themes and navigation paths, especially for permalink and sharing flows.