Add repository-level project and workspace manifest discovery

[abhinavgautam01]

Closes #55

Summary

• Add a rooted RepositoryReader API for repository-level manifest discovery.
• Add an FSReader adapter supporting recursive glob patterns over fs.FS.
• Discover registered manifests and lockfiles at the repository root.
• Discover GitHub Actions workflows under .github/workflows.
• Discover workspace members declared by:
  • Cargo workspaces, including exclusions
  • Go workspaces through go.work
  • npm and Yarn workspace configurations
  • pnpm workspace patterns and exclusions
• Retain the selecting workspace configuration in DiscoveredManifest.ParentPath.
• Return normalized, deterministic discovery results while rejecting paths outside the repository root.
• Keep the existing single-file Parse API unchanged.

Implementation

Go workspace files are parsed using golang.org/x/mod/modfile. Recursive workspace patterns are resolved using doublestar, allowing the same discovery API to work over operating-system directories and historical Git-tree readers.

Malformed workspace configurations and reader failures are returned with contextual errors instead of silently producing incomplete results.

Testing

Added regression coverage for:

• Root manifests, lockfiles, and path-based GitHub Actions workflows
• Cargo members and exclusions
• Quoted and unquoted go.work entries
• npm array and Yarn object workspace formats
• Recursive pnpm patterns and exclusions
• Workspace parent provenance
• Repository path traversal rejection
• Invalid workspace configuration and reader errors

Verification

• go build ./...
• go mod tidy -diff
• go test ./... -count=1
• go test -race ./... -count=1
• golangci-lint run ./...