Add project-aware chat startup defaults

Make repo-root chat startup native by letting MCP servers carry a default project source for workspace creation. When a chat host starts from a Git checkout, workspace_create can now omit seed_path and inherit the server startup source; explicit --project-path and clean-clone --repo-url/--repo-ref paths are supported as fallbacks.

Add project startup resolution and materialization, surface origin_kind/origin_ref in workspace_seed, update chat-host docs and the repro/fix smoke to use project-aware workspace creation, and switch dist-check to uv run pyro so verification stays stable after uv reinstalls.

Validated with uv lock, focused startup/server/CLI pytest coverage, UV_CACHE_DIR=.uv-cache make check, UV_CACHE_DIR=.uv-cache make dist-check, and real guest-backed smokes for both explicit project_path and bare repo-root auto-detection.

docs/public-contract.md

@@ -76,10 +76,16 @@ pyro mcp serve
 What to expect:
 
 - bare `pyro mcp serve` starts `workspace-core`
+- from a repo root, bare `pyro mcp serve` also auto-detects the current Git
+  checkout so `workspace_create` can omit `seed_path`
 - `workspace-core` is the default product path for chat hosts
 - `pyro mcp serve --profile workspace-full` explicitly opts into the larger
   tool surface
 - `pyro mcp serve --profile vm-run` exposes the smallest one-shot-only surface
+- `pyro mcp serve --project-path /abs/path/to/repo` is the fallback when the
+  host does not preserve cwd
+- `pyro mcp serve --repo-url ... [--repo-ref ...]` starts from a clean clone
+  source instead of a local checkout
 
 Host-specific setup docs:
 
@@ -111,7 +117,8 @@ Host-specific setup docs:
 
 That is enough for the normal persistent editing loop:
 
-- create one workspace
+- create one workspace, often without `seed_path` when the server already has a
+  project source
 - sync or seed repo content
 - inspect and edit files without shell quoting
 - run commands repeatedly in one sandbox