Support WebFetch Skill across multiple agents

[mayuqin746]

What changed

• resolve the WebFetch Skill across Codex, Claude Code, and WorkBuddy/CodeBuddy installations
• make Skill instructions and references use host-provided Skill roots and Skill-local absolute commands
• default OAuth client_name to Agent, preserve Agent-specific names, and URL-encode them safely
• make doctor validate the complete eight-file Skill ZIP, report every discovered candidate, and return stable JSON for missing or corrupt credentials
• remove the legacy partial skill install/status flow so installation follows the host-managed Skill ZIP contract
• bump the CLI and bootstrap version to 0.1.3
• add current-source Windows testing and static CRT verification

Why

The previous Skill and CLI behavior assumed WorkBuddy or Codex-specific paths, did not discover Claude Code installations consistently, and could install only a partial embedded Skill that did not match the release ZIP. Authentication guidance also used a fixed Agent identity and PATH-based repair commands.

This change aligns WebFetch with the multi-Agent, Skill-local release model used by Browser CLI while retaining compatibility discovery paths where they are safe.

User and developer impact

• Codex, Claude Code, and WorkBuddy can use the same Skill package.
• Login approval pages receive the correct Agent name, with Agent as the fallback.
• doctor --json distinguishes the current Skill from fallback installations and reports incomplete ZIP contents precisely.
• Skill installation is owned by the Agent host; the CLI no longer exposes the incompatible legacy installer.

Validation

• cargo fmt --all -- --check
• cargo test --all-targets --locked (27 tests)
• cargo clippy --all-targets --locked -- -D warnings
• cargo build --bin webfetch-cli --locked
• Skill structure validation and Skill-local doctor forward test
• deterministic Skill ZIP verified across repeated builds with exactly eight files
• workflow YAML and shell syntax validation