feat(peer): prototype streamed installs

Add a streamed-install prototype that can receive archive-derived install bytes
straight into local/ without first storing the peer-owned root archive payload.
This is intended for low-disk clients that want to install a game but opt out of
becoming a downloadable peer source for that game.

The protocol gains a current-version-only StreamInstall request and framed
StreamInstallFrame responses. The peer core owns the generic transport,
transaction, path validation, size checks, CRC32 verification, and lifecycle
state. The archive-specific work is hidden behind StreamInstallProvider so the
prototype can use unrar while the final implementation can swap in a better
provider without rewriting the peer command path.

The receiver writes into .local.installing and only promotes to local/ after the
full stream verifies. It deliberately does not write the root version.ini or
archive files, so the settled local state is installed=true, downloaded=false,
and availability=LocalOnly. That preserves the existing rule that local/ is not
served to peers and makes streamed receivers non-sources by construction.

The CLI is the only caller for now. It exposes stream-install and provides the
prototype unrar implementation with unrar lt for entry metadata and unrar p for
file bytes. This is simple and good enough to prove non-solid archive streaming,
but it is not the production provider shape for solid archives because per-file
unrar p would repeatedly decompress prefixes. The Tauri app explicitly passes
stream_install_provider: None, so the GUI behavior stays unchanged until a real
product path is designed.

Document the production-readiness work in NEXT_STEPS.md. The main follow-up is
to make the provider abstraction final-ish and replace the per-file CLI unrar
provider with a one-pass archive provider, then wire a deliberate GUI low-disk
mode, retry semantics, and broader failure scenarios.

Test Plan:
- just fmt
- RUSTC_WRAPPER= CARGO_BUILD_RUSTC_WRAPPER= just test
- python3 crates/lanspread-peer-cli/scripts/run_extended_scenarios.py \
  S39 S40 --build-image
- RUSTC_WRAPPER= CARGO_BUILD_RUSTC_WRAPPER= just clippy
- git diff --check
- git diff --cached --check

Follow-up: NEXT_STEPS.md

crates/lanspread-peer-cli/Cargo.toml

@@ -14,11 +14,14 @@ path = "src/main.rs"
 lanspread-compat = { path = "../lanspread-compat" }
 lanspread-db = { path = "../lanspread-db" }
 lanspread-peer = { path = "../lanspread-peer" }
+lanspread-proto = { path = "../lanspread-proto" }
 
+bytes = { workspace = true }
 eyre = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
 tokio = { workspace = true }
+tokio-util = { workspace = true }
 
 [lints.clippy]
 needless_pass_by_value = "allow"