Create a single-file browser-based casefile benchmark called "Bathysphere Nine: The Vanishing Dive" for the canonical `/casefile/` route in a one-shot catalog.

Case brief:
- The user is investigating the disappearance of the research bathysphere *Pelican-9*, which lost contact during a descent to map a trench anomaly known as the Choir Step.
- The interface should feel like a lived-in evidence wall assembled by an exhausted marine incident analyst over five sleepless nights.
- The investigator's goal is to trace how a falsified maintenance clearance, a route deviation, and an unlogged private transmission connect to the vessel's disappearance.

Evidence model:
- Use at least 10 evidence cards across at least 4 evidence types:
  - mission logs
  - sonar or depth telemetry
  - personnel notes and interview fragments
  - maintenance records
  - private comms or memo excerpts
- Include a timeline view that shows the final 36 hours around the dive.
- Include a clue graph or linked-cards mechanic that makes the connection trail explicit.
- Include a focused reading pane with long-form document text, tags, and contradiction markers.

Reveal logic:
- The starting board should show uncertainty, not the answer.
- Users can open cards, pin cards, filter by evidence type, and trace relationships.
- Progress must persist in localStorage, including opened cards, pinned cards, and solved-state flags.
- The critical reveal should unlock only after the user has inspected the forged ballast seal memo, the route offset telemetry, and the private "hold descent window" transmission.
- Once those three pieces are discovered, the board should mark the case as solvable and surface the conclusion that the dive was redirected to investigate an off-book signal despite known hull-risk warnings.

Visual direction:
- Moody salvage-room palette with oxidised brass, sonar cyan, emergency amber, and paper-dust neutrals.
- The desktop view should resemble a layered evidence wall with strings, cards, and a central detail pane.
- Mobile must switch to an alternate tabbed investigation layout rather than simply shrinking the wall.
- Keep typography sans-serif and screen-readable. Avoid novelty detective fonts.

Implementation constraints:
- Single `index.html` only, with inline CSS and JS.
- Vanilla JS only.
- Deliver a polished, navigable benchmark artifact rather than a static mockup.