Fast /drivers path (static roster index) to remove the FastF1-parse wait

[VforVitorio]

Problem

After the user picks a session, the DRIVERS combobox is unusable for the ~2-15s it takes FastF1 to parse the session behind GET /api/v1/telemetry/drivers. PR #95 added a loading affordance (spinner + aria-busy + "Loading drivers…") so it reads as working rather than broken — but the underlying wait is still there.

Proposal

Serve the driver roster (and GP/session lists) from a static index committed to the repo, with a FastF1 fallback for anything not in the index:

• backend/scripts/build_telemetry_index.py → backend/static/telemetry_index.json (2022-2025 rosters/GPs/sessions frozen).
• get_available_gps / get_sessions / get_drivers become a dict lookup first, FastF1 fallback second.
• Turns a seconds-long list into a <5ms response; the session still parses lazily on the first telemetry request (prewarm already covers that).

Notes

• The /prewarm endpoint (PR perf(telemetry): reuse loaded FastF1 sessions + non-blocking endpoints #91) already warms the FastF1 session cache on session-select, so telemetry is fast; this issue is specifically about the roster list latency.
• Non-blocking follow-up to the round-2 dashboard work (see docs/migration/design-specs/dashboard-round2.md item 2).