patch: Make find_project_root() recognize all project types

[rdwj]

Problem

find_project_root() in tools/validation.py only recognizes MCP server projects by checking for a fastmcp dependency in pyproject.toml. Agent projects (which depend on fipsagents), Go-based projects (gateway/ui), and sandbox projects all return None, causing every patch subcommand to fail with "Not in a project directory."

Proposed change

Instead of detecting the project type from pyproject.toml dependencies, look for the .template-info file. Any project scaffolded by fips-agents create writes this file, so it's a universal marker.

Options (pick one):

Option A — New function for patch context: Add find_fips_project_root() that walks up the directory tree looking for .template-info. Leave the existing find_project_root() for MCP-specific commands (add, generate) that genuinely need to confirm the project is an MCP server.

Option B — Generalize find_project_root(): Add an optional project_type parameter. Default behavior checks for .template-info. Pass project_type="mcp-server" from add/generate commands to keep the fastmcp check.

Option A is simpler and avoids breaking existing callers.

Part of

Tracking issue: #12
Depends on: #13 (.template-info needs template.type for the patch system to select the right behavior, but the root-finding itself just needs the file to exist)