feat: initial repo setup (Phase 0 scaffolding)

- AGENTS.md: repo conventions adapted from alkcall/alksocks (store
  posture, multi-hash requirement, no-iroh-wire rule; no fuzz gate yet)
- Cargo.toml + src/lib.rs: bare lean lib skeleton (tokio async, thiserror)
- docs/research/phase-0.md: Phase 0 draft — vision, prior art (iroh-blobs
  store, gix-odb, alknet appfile probe, alkcall), OQ register, POC plan
- .gitignore, LICENSE-APACHE/MIT
- Re-pointed stale alknet/alkcall references in .opencode/agents/ and
  docs/sdd_process.md

Verification: cargo build/test, cargo clippy --all-targets -- -D
warnings, cargo fmt --check, cargo doc --no-deps — all pass

src/lib.rs

@@ -0,0 +1 @@
+pub fn placeholder() {}