Feature: True full-text index (FTS5) and exact-match mode

[bwl]

Status Update

Reframing scope:

• Remote metadata search parity is already present.
• This issue should focus on true full-text indexing and exact-match retrieval quality.

Proposal (refined)

• Add SQLite FTS5 index for title/body
• Add a dedicated full-text search path/mode for exact phrase and lexical queries
• Support phrase queries, token matches, and predictable relevance ordering
• Keep semantic search as a separate complementary mode

Why this matters

Semantic retrieval is great for conceptual similarity; we still need exact lexical retrieval for precision workflows.