`manage_adr` (MCP/CLI) and the UI `/api/adr` endpoints use separate storage backends

[bschrib]

The MCP tool manage_adr writes/reads ADRs as files at <root>/.codebase-memory/adr.md. The HTTP UI's /api/adr endpoints read/write SQLite via cbm_store_adr_get / cbm_store_adr_store. Writes via either interface are invisible to the other.

Reproduction (v0.6.0, macOS arm64):

# write via CLI
codebase-memory-mcp cli manage_adr '{"project":"<name>","mode":"update","content":"## PURPOSE\ntest\n"}'

# CLI roundtrips
codebase-memory-mcp cli manage_adr '{"project":"<name>","mode":"get"}'   # -> returns content
cat <repo>/.codebase-memory/adr.md                                         # -> content present

# UI endpoint
curl http://localhost:9749/api/adr?project=<name>                          # -> {"has_adr": false}

The UI's + ADR button stays + ADR because hasAdr comes from that /api/adr response (graph-ui/src/components/StatsTab.tsx:111).

Code pointers:

• src/mcp/mcp.c:3498-3555 — handle_manage_adr, file-backed at <root>/.codebase-memory/adr.md.
• src/ui/http_server.c:449-559 — handle_adr_get / handle_adr_save, SQLite-backed via cbm_store_adr_* (src/store/store.c:4537,4560).

Expected: one canonical backend. The file-on-disk path is likely the right target since it's committable and lives with the repo; the SQLite-backed UI handlers would need to switch to reading/writing the file.

Impact: ADRs created by agents via MCP don't surface in the graph UI. ADRs created by humans in the UI aren't readable by agents.