Community task: Contributor documentation improvements

[codethor0]

Background

Ghost Sweep is opening broader community participation. Documentation should help new contributors find safe lanes quickly.

Scope

• Improve cross-links among README, CONTRIBUTING, GOVERNANCE, contributor onboarding, and reporting policy docs
• Fix stale references (for example old commit SHAs or outdated collaborator notes)
• Add short start-here guidance for first-time contributors
• Update docs/labels.md if label usage examples need refresh

Acceptance criteria

• Docs-only change set
• No contradictory guidance versus AGENTS.md or GOVERNANCE.md
• Links resolve to existing files

Test / validation

• Manual review of changed markdown
• git diff --check

Non-goals

• No API, schema, CI, or runtime behavior changes
• No new dependencies

Privacy constraints

• No private submission examples

Approval-required boundaries

• Do not change security, privacy, or import policy without project-owner review