GD-2383: Add Harness for Givesource (KB, workflows, skills, AGENTS.md)

[cjasonbush]

This PR introduces a Givesource-specific Harness to ground AI agents on long-running tasks via structured workflows, a central knowledge base, and append-only tracking.

Highlights

• Harness structure and KB
  • harness/README.md
  • harness/repo-config.yml (packages, commands, deploy runbooks, invariants, workflows incl. kb_update)
  • harness/givesource.md (repo-specific KB; replaces ai-search)
  • adrs/: README + adr-0000-template
  • plans/, checkpoints/, amendments/: README guides
• Workflows (.devin/workflows)
  • harness-plan.md, harness-checkpoint.md, harness-amend.md, harness-adr.md, harness-kb-update.md
  • Fix ADR workflow header; robust ADR numbering
• Repo-wide grounding for agents
  • AGENTS.md at root
  • README: new "For AI agents" section with links
• Skills (.devin/skills)
  • plan/, story/, review/, pr/, pr-comments/, merge/ — repo-specific launchers that resolve this repo, load harness/repo-config.yml, and include fallbacks if external plugins are unavailable
• Cleanups
  • Replace all references to ai-search with givesource
  • Remove harness/ai-search.md

Meta

• Branch: feature/GD-2383-harness (from develop)
• Version bump: package.json 4.2.21 -> 4.2.22
• Jira: GD-2383

Acceptance

• Harness folder exists and is repo-specific
• AGENTS.md published with directives
• Skills/workflows wired to harness/repo-config.yml
• README links to AGENTS.md and KB
• Jira updated; branch open; version bumped