fix: address all critical (P0) security findings

[hybridindie]

Summary

• Client _request hardening: Replaced getattr(c, method) dynamic dispatch with c.request(normalized, path) using httpx's official API, guarded by _ALLOWED_HTTP_METHODS frozenset
• URL path traversal prevention: Added _validate_prompt_id() (UUID regex) and _validate_path_segment() for all URL-interpolated parameters (prompt_id, node_class, task_id)
• Input mutation fix: Removed node_data["inputs"] = {} in validate_workflow that was mutating the caller's dict and could mask injection patterns before the workflow inspector runs
• SSE transport warning: Added field_validator on SSESettings.host that logs a warning when SSE is bound to non-localhost (no auth mechanism exists)
• Docker non-root: Container now runs as dedicated app user instead of root
• GitHub Actions pinning: All actions in ci.yml and docker.yml pinned to full commit SHAs

Test plan

• All 351 tests pass
• ruff check clean
• ruff format --check clean
• mypy clean
• All pre-commit hooks pass
• Verify CI passes on GitHub

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Security hardening PR that addresses P0 findings: hardens HTTP dispatch in the client, adds URL path traversal prevention via input validation, removes an input mutation bug in workflow validation, warns on non-localhost SSE binding, and improves Docker/CI security posture.

Changes:

• Replaced dynamic getattr HTTP dispatch with c.request() guarded by an allowlist, and added UUID/path-segment validation for URL-interpolated parameters
• Removed node_data["inputs"] = {} mutation in validate_workflow and added SSE host warning validator
• Pinned GitHub Actions to commit SHAs and switched Docker container to non-root user

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/comfyui_mcp/client.py	Added HTTP method allowlist, UUID validation, and path segment validation for URL parameters
src/comfyui_mcp/workflow/validation.py	Removed input mutation that could mask injection patterns
src/comfyui_mcp/config.py	Added field_validator warning for non-localhost SSE binding
Dockerfile	Added non-root app user
.github/workflows/ci.yml	Pinned actions to commit SHAs
.github/workflows/docker.yml	Pinned actions to commit SHAs
tests/*	Updated test prompt IDs to valid UUID format matching new validation

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[Copilot]

The groupadd/useradd commands should be run before COPY and RUN uv sync so that the user creation layer is cached independently of source changes. Also, since files were copied as root, the app user may not have read access to /app. Consider adding --chown=app:app to the COPY directives or running chown before switching to USER app.