chore(workflows): upgrade gh-aw to v0.76.1

[jamesadevine]

Summary

Refresh the agentic-workflows dispatcher agent and recompile all .github/workflows/*.lock.yml against gh-aw v0.76.1 (previously v0.75.3). Done by running gh aw upgrade --no-fix followed by gh aw compile, plus pruning one orphaned entry from actions-lock.json.

What changed

• .github/agents/agentic-workflows.agent.md — re-downloaded the canonical v0.76.1 dispatcher; all 17 prompt URLs re-pinned v0.75.3 → v0.76.1. This is the centralised routing/dispatch agent that replaces the per-task agent files (create-agentic-workflow.agent.md, debug-agentic-workflow.agent.md, etc.) — none of those legacy files existed in this repo.
• .github/workflows/copilot-setup-steps.yml — github/gh-aw-actions/setup-cli bumped v0.68.1 → v0.76.1 so Copilot Cloud installs the matching CLI.
• .github/workflows/*.lock.yml (16 workflow lock files) — recompiled with gh-aw v0.76.1. Notable upstream changes pulled in:
  • github/gh-aw-actions/setup bumped to v0.76.1
  • gh-aw-firewall/{agent,api-proxy,squid} images bumped to 0.25.55
  • gh-aw-mcpg bumped to v0.3.19
  • github-mcp-server:v1.0.4 now pinned by digest
  • node:lts-alpine digest pin refreshed
  • Sparse-checkout / save / restore now also covers .antigravity and .github/skills
  • New Restore inline skills from activation artifact step
  • detect-copilot-errors step renamed to detect-agent-errors (output names updated accordingly)
  • Default Copilot model bumped to claude-sonnet-4.6
• .github/aw/actions-lock.json — bumped github/gh-aw-actions/setup to v0.76.1 and removed the now-orphaned github/gh-aw/actions/setup@v0.68.1 entry (legacy repo path; no workflow referenced it after the setup-cli bump).

Test plan

• gh aw upgrade --no-fix ran clean and reported Upgrade complete.
• python3 -c "import json; json.load(open('.github/aw/actions-lock.json'))" confirms the lock file is valid JSON after pruning.
• grep -rn "v0.68.1\|github/gh-aw/actions/setup" .github/ returns no matches.
• grep -c "blob/v0.76.1" .github/agents/agentic-workflows.agent.md returns 17, and grep -c "blob/v0.75.3\|blob/main/" … returns 0.
• No Rust source or tests changed — cargo validation isn't required for this PR.