Enhancement: Restrict daily totals to portable assets and stable releases (configurable)

Summary
Current implementation sums all assets for all fetched releases. To answer “how many downloads of the portable releases per day,” we should filter assets by name pattern and optionally exclude prereleases/drafts via configuration.

Details
- All assets inserted: scripts/fetch-data.mjs:317–333
- Daily totals don’t filter by flags: scripts/fetch-data.mjs:343–357

Proposed Fix
- Add env flags:
- PORTABLE_ONLY=true
- PORTABLE_NAME_PATTERN=ComfyUI_windows_portable_
- INCLUDE_PRERELEASE=false
- INCLUDE_DRAFT=false
- In storeDailyStats, skip releases when draft/prerelease if flags are false; skip assets not matching pattern when PORTABLE_ONLY=true.
- Optionally enforce the same filter in the summary SQL for safety.

Acceptance Criteria
- Changing flags alters which asset rows are stored for the bucket
- Daily totals reflect only portable, stable releases by default

References
- Asset loop: scripts/fetch-data.mjs:317–333
- Summary calculation: scripts/fetch-data.mjs:343–357