feat: use right-aligned dashboard Markdown icons - #499

Summary

Dashboard Markdown source links now appear as small document icons at the right of their heading or utility row. Section icons follow the badges, leaving the heading clear while retaining the original destination.

The shared layout applies this to existing “markdown version” links when boards regenerate. Each icon has a tooltip, accessible name, visible keyboard focus and a 44px click target. Other Markdown links remain unchanged.

Validation

• Shared-theme, section, Mind, Brain and Cortex renderer checks: 271 passed.
• Browser checks across 390, 768, 820, 1024 and 1440px in light and dark mode; no overflow; existing navigation and disclosure behavior preserved.
• All seven Mind source links retain their URLs; mouse and keyboard activation reaches the destination without toggling a section.
• Full Brain suite: 1270 passed; the remaining grouped-root fixture passes with PYAUTO_MIND unset (4/4 grouped checks pass). The generated activation override was leaking into the fictional fixture.
• Mind suite: 695 passed; the remaining root fixture passes with worktree root overrides unset (7/7 root checks pass).
• Heart YELLOW acknowledged by the human on 2026-10-07: “manifest drift: workspace checkouts (manifest ↔ disk) — 3 mismatch(es) vs PyAutoMind/repos.yaml”; “release validation incomplete: no rehearsal for current source”. Reasons unchanged at shipping.

API Changes

None — internal presentation change. Board owners retain their destinations and data. Consumers receive the icons on their next regeneration with the updated shared theme.

Closes #498.