Refactor OPENASTROVIZD_SOCKET readiness parsing to explicit URI schemes

[seanwevans]

Motivation

• The previous readiness check inferred protocol from target.contains(':'), which was brittle and misclassified Windows paths and other inputs.
• Require explicit URI schemes to make readiness checks deterministic and easier to validate at startup.
• Support both TCP and filesystem/unix socket readiness semantics with platform-aware handling for Windows drive-letter paths.

Description

• Replace ad-hoc inference with a typed ReadinessTarget enum and a parse_readiness_target function that accepts tcp://, unix://, and file:// URIs.
• Validate tcp:// addresses using ToSocketAddrs and normalize filesystem URIs with path_from_uri (including Windows drive-letter handling), and expose readiness checks via readiness_target_ready used from wait_for_readiness.
• Make the old socket_ready helper test-only and add unit tests covering scheme-required behavior and parser acceptance/rejection cases.
• Update README.md, daemon/README.md, and daemon/openastrovizd/README.md to document the accepted OPENASTROVIZD_SOCKET formats with examples.

Testing

• Ran cargo test -p openastrovizd parse_readiness_target, which executed parser tests and passed (2 passed).
• Ran cargo test -p openastrovizd socket_ready_requires_scheme, which passed (1 passed).
• Attempted cargo fmt --all but formatting failed in this environment because rustfmt is not installed for the active toolchain.

---

Codex Task