Split [server/dashboard/_page.py](hackagent/server/dashboard/_page.py) (6,535 lines) into per-component files

[franconicola]

Problem. A single 6.5 kLOC file is unreviewable, hard to test, and tightly couples UI components to one another.

Actions.

• Identify natural component boundaries (one nicegui "page" or "card" per file).
• Extract data-loading and aggregation out of the page into server/dashboard/_api.py (which already exists) so each component receives plain dicts/dataclasses.
• Move each component into server/dashboard/components/<name>.py.
• Cap individual files at ≤500 lines.
• Add at least smoke tests that each component module imports cleanly.

Acceptance: no file in server/dashboard/ exceeds 500 lines; _page.py becomes a thin assembler.