Add search and owner filtering to repos table

[larsborn]

Adds filtering controls above the repos table on the home page:

• Text search input (case-insensitive substring match on repo name, 300ms debounce via HTMX)
• Owner/org dropdown (filters by owner/ prefix, only shown when more than one owner exist)

Both filters compose with each other and preserve the current sort column/direction across interactions using hidden inputs with HTMX out-of-band swaps. The REST API also accepts the new q and owner query parameters.

Closes #22

[vladkens]

Thanks for the contribution. I'm going to merge this PR, and I'll follow up shortly with a new release that includes it.

[larsborn]

Thanks a ton for the quick response and release!