feat(github-copilot): add GitHub Copilot (VS Code) integration via MCP

[DK09876]

Summary

Adds a first-party GitHub Copilot (VS Code) integration for Hindsight, using Copilot agent mode's native MCP support (HTTP servers) — so Hindsight connects directly, no bridge.

hindsight-copilot init:

• merges a Hindsight HTTP MCP server into .vscode/mcp.json (servers.hindsight), and
• writes a recall/retain rule into .github/copilot-instructions.md, which Copilot applies to every chat in the workspace.

{ "servers": { "hindsight": { "type": "http", "url": "https://api.hindsight.vectorize.io/mcp/my-project/", "headers": { "Authorization": "Bearer hsk_..." } } } }

Resolves the ask in #1588 ("Vscode/GitHub Copilot Integration"). Mirrors the Zed/OpenHands MCP-config pattern.

What's included

• hindsight_copilot package: config, mcp_config (.vscode/mcp.json writer — JSON round-trip, prints a snippet for JSONC files), instructions (fenced-block rule writer), cli (init/status/uninstall).
• 25 deterministic tests: .vscode/mcp.json merge (preserving other servers + inputs, JSONC → manual fallback, dedup) and the copilot-instructions.md rule block. Plus a gated requires_real_llm E2E doing the real MCP initialize handshake against a live server.
• CI job test-github-copilot-integration + detect-changes + aggregation.
• Release registration in VALID_INTEGRATIONS and the changelog generator.
• Docs page, registry entry, icon (octicons), README row.

Testing

• 25 deterministic tests pass; ruff check/format clean (repo ruff.toml); uv build + uv lock --check consistent.
• Gated E2E verified against a live local Hindsight (MCP handshake → tools/list returns recall/retain/reflect).

🤖 Generated with Claude Code

[benfrank241]

@DK09876 nice work, this one's clean. addresses #1588 — going native MCP HTTP over the hooks approach scott suggested is the right call (cleaner, fewer moving parts, matches the zed/openhands pattern).

two things before merging:

needs a rebase — github shows CONFLICTING. main moved since you opened it.
Build Docker (control-plane) failed but it's unrelated to this python-only integration. should clear on the rebase re-run; if not, re-run that job.
the jsonc → manual-snippet fallback and the fenced HINDSIGHT:BEGIN/END rule block are both nice touches — preserves user content on uninstall and won't clobber commented .vscode/mcp.json files. static "copilot" bank default matches the existing zed/openhands pattern so that's consistent (--bank-id override is documented).