match_seeds() previously only found nodes whose keys exactly matched
search terms. This meant searches like "formal verification" or
"bcachefs plan" returned nothing — no nodes are keyed with those
exact strings.
Three-tier matching strategy:
1. Exact key match (full weight) — unchanged
2. Key component match (0.5× weight) — split keys on -/_/./#,
match individual words. "plan" now finds "the-plan", "verification"
finds "c-to-rust-verification-workflow", etc.
3. Content match (0.2× weight, capped at 50 hits) — search node
content for terms that didn't match any key. Catches nodes whose
keys are opaque but whose content is relevant.
Also adds prompt-based seeding to the hook pipeline: extract_query_terms
from the user's prompt and merge into the term set. Previously the hook
only seeded from transcript scanning (finding node keys as substrings
in conversation history), which meant fresh sessions or queries about
new topics produced no search results at all.