kb-server: add deterministic context retrieval APIs

[yashomdighe]

Build read-only /context/search and /context/bundle endpoints over main/current views, with ranked matches, excerpts, and provenance for agent workflows.

Address #2

Topic: retrieval-layer

[yashomdighe]

Reviews in this chain:
└#9 kb-server: add deterministic context retrieval APIs
　└#10 mcp-server: expose Flight Deck retrieval and note tools via MCP

[yashomdighe]

#	head	base	diff	date	summary
0	7cbd8596	7c47d50b	diff	Mar 12 8:37 AM	12 files changed, 889 insertions(+), 6 deletions(-)
1	eda22d51	7c47d50b	diff	Mar 12 8:47 AM	0 files changed
2	de3092e4	7c47d50b	diff	Mar 12 20:58 PM	2 files changed, 8 insertions(+), 4 deletions(-)
3	426737a7	7c47d50b	diff	Mar 12 21:40 PM	3 files changed, 41 insertions(+), 15 deletions(-)