Move MicroPlex storage config to PolicyEngine

[MaxGhenis]

Summary

• prefer PolicyEngine-owned Supabase env vars for MicroPlex scripts while retaining legacy fallbacks
• remove the hard-coded old Supabase project URL from calibration loaders
• update repo metadata, badges, docs URLs, and generated dashboard link to PolicyEngine ownership

Supabase follow-up

• checked the shared credentials docs available through Google Drive; I did not find a PolicyEngine Supabase API/service key there
• found the existing PolicyEngine Supabase project policyengine-strategy (naalkftuqvyhjpvwlvnd), but Supabase reports it as INACTIVE and refuses restore because it has been paused for more than 90 days
• did not leave GitHub repo variables/secrets pointing to that dead project

Tests

• uv run python -m py_compile scripts/load_pe_targets.py scripts/run_supabase_calibration.py scripts/build_block_geography.py tests/test_supabase_client.py
• uv run ruff check --select F821 scripts/load_pe_targets.py scripts/run_supabase_calibration.py scripts/build_block_geography.py tests/test_supabase_client.py
• uv run --extra dev python -m pytest tests/test_supabase_client.py -q

Note: Full ruff on the touched script files is blocked by existing broad lint debt in those files; this PR ran syntax, undefined-name, and targeted tests instead.