bild: support local runtime deps (-- : run Omni/Task.hs)

Add support for local omnirepo dependencies in bild runtime deps.

Goal

Enable -- : run Omni/Task.hs to include local binaries in PATH.

Approach

1. Distinguish local vs external rundeps in Meta.hs (by file extension or path pattern) 2. Add local rundeps to build queue automatically 3. After building, read store paths from _/nix/ symlinks 4. Pass paths to Builder.nix for wrapProgram

Files to modify

• Omni/Bild/Meta.hs: Add LocalRun vs ExternalRun types
• Omni/Bild.hs: Extract local rundeps, add to build queue, pass paths
• Omni/Bild/Builder.nix: Accept localRundepPaths and include in PATH

Test case

-- In Omni/Ava.hs:
-- : run Omni/Task.hs

-- Should result in task binary being in Ava's PATH

See design doc: _/tmp/local-rundeps-design.md