feat: improve search relevance, add pagination, and clean up legacy templates

[Pierre-VF]

Description:

This PR delivers several improvements to the search experience and UI, along with cleanup of legacy code.

Search improvements

• Field-weighted keyword search: Results now rank by field importance — name (weight 5) > organisation (4) > description (3) > readme (2) — so title matches surface first.
• Hybrid search support: When enabled, embeddings are combined with keyword search using rerank_hybrid_matches and a vector query on embedding_description. Includes a graceful fallback to keyword-only search if embeddings are not yet available.
• Typo tolerance & prefix matching: Enabled to make search more forgiving of typos and partial queries.
• Case-insensitive search preserved: Query normalization now strips whitespace without lowercasing, delegating case handling to Typesense.

Pagination

• Added pagination UI with "Previous" / "Next" buttons on the results page.
• Backend computes total pages and preserves all query parameters (except offset) across page navigation.

UI polish

• Source count badges now display tiered colors: gold (>1000 projects), silver (>50), bronze (otherwise).
• GitHub icon added to the navbar as a visual link to the repository.

Cleanup

• Removed legacy v1 templates (_base.html, _navbar.html, results.html) no longer in use.
• Removed truncated readme field from Typesense import to save memory.
• Disabled commented-out hybrid search params in search_for_url.

Dependencies & config

• Bumped version to 0.9.3.
• Upgraded sentry-sdk[fastapi] from >=2.58.0 to >=2.61.1.
• Added seed_typesense target to the Makefile.
• Added rebase-energy/timedb to the indexed repositories.