feat: workspace skeleton + phase 0 research docs

- Cargo workspace with 5 sub-crates: alkgit-core (storage),
  alkgit-transport (smart protocol), alkgit-http, alkgit-ssh, alkgitd
  (binary); sha1 pinned through the gix stack, sha256 passthrough feature
- docs/research/: vision, gitoxide alignment, alk stack fit, server-side
  protocol inventory, license/reference policy, POC plan
- AGENTS.md: conventions mirroring alkcall (no comments, thiserror, tokio,
  no secrets on wire/at rest, visible-surface=authorized-surface,
  gitoxide-only serving path, bounded resources, registry-resolved repos)

Verified: cargo build, clippy -D warnings, fmt, test, check --all-features

crates/alkgitd/Cargo.toml

@@ -0,0 +1,31 @@
+[package]
+name = "alkgitd"
+description = "The alkgit server binary: assembles storage, smart protocol, HTTP, SSH, and TLS into one self-hosted git server"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+repository.workspace = true
+
+[[bin]]
+name = "alkgitd"
+path = "src/main.rs"
+
+[dependencies]
+alkgit-core = { workspace = true }
+alkgit-transport = { workspace = true }
+alkgit-http = { workspace = true }
+alkgit-ssh = { workspace = true }
+alkhttp = { workspace = true }
+alktls = { workspace = true }
+alkvault = { workspace = true }
+tokio = { workspace = true }
+serde = { workspace = true }
+tracing = { workspace = true }
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+thiserror = { workspace = true }
+
+[features]
+default = []
+sha256 = ["alkgit-http/sha256"]
+acme = ["alktls/acme"]