feat: deploy script should auto-detect sqlite-vec extension path

[quanyeomans]

Problem

SQLITE_VEC_PATH must be set in service.env for vector search to work. The deploy script does not set this variable — the operator must find the .so file manually and add it.

On the current VM, it lives at:

/data/tools/qmd/node_modules/.pnpm/sqlite-vec-linux-x64@0.1.7-alpha.2/node_modules/sqlite-vec-linux-x64/vec0.so

This path is not documented anywhere in the repo and is discovered only through trial and error.

Proposed Fix

Add auto-detection logic to the deploy script (or a post-install check in kairix onboard check):

# Common probe locations in priority order
PROBE_PATHS=(
    "/usr/local/lib/vec0.so"
    "/usr/lib/sqlite-vec/vec0.so"
    /data/tools/qmd/node_modules/.pnpm/sqlite-vec-linux-x64@*/node_modules/sqlite-vec-linux-x64/vec0.so
    /opt/*/vec0.so
)

for path in "${PROBE_PATHS[@]}"; do
    expanded=$(echo $path)  # glob expansion
    if [[ -f "$expanded" ]]; then
        echo "SQLITE_VEC_PATH=$expanded" >> /opt/kairix/service.env
        break
    fi
done

If not found, emit a clear warning:

WARNING: sqlite-vec extension not found. Vector search will be unavailable.
Install sqlite-vec and set SQLITE_VEC_PATH=/path/to/vec0.so in /opt/kairix/service.env

Acceptance Criteria

• Deploy script sets SQLITE_VEC_PATH automatically when the extension can be found
• If not found, deploy script prints actionable install instructions
• kairix onboard check vector search check reports the probed path when diagnosing failures