feat: add multi-tool integration scripts and converted agent files

Adds support for installing The Agency agents across 7 agentic coding
tools via two scripts:

scripts/convert.sh
  - Reads all 61 agents and converts them into tool-specific formats
  - Supports: Antigravity, Gemini CLI, OpenCode, Cursor, Aider, Windsurf
  - Shellcheck-clean, pure bash, no external deps
  - Run: ./scripts/convert.sh [--tool <name>]

scripts/install.sh
  - Interactive terminal UI with auto-detection of installed tools
  - Pre-selects detected tools, toggle by number or bulk commands
  - Falls back gracefully in CI / non-interactive mode
  - Cross-platform: Linux, macOS (bash 3.2+), Windows Git Bash / WSL
  - Run: ./scripts/install.sh [--tool <name>] [--no-interactive]

integrations/ (generated, committed for reference)
  - antigravity/   SKILL.md per agent (61 files)
  - gemini-cli/    SKILL.md per agent + gemini-extension.json
  - opencode/      .md agent files for .opencode/agent/
  - cursor/        .mdc rule files for .cursor/rules/
  - aider/         single CONVENTIONS.md (all agents combined)
  - windsurf/      single .windsurfrules (all agents combined)
  - claude-code/   README only (agents copied directly from repo root)
  - README.md      full usage + tool-specific instructions

README.md
  - Added Multi-Tool Integrations section with supported tools table,
    quick-start guide, per-tool expandable instructions, and updated
    roadmap marking integrations as complete

integrations/cursor/README.md

@@ -0,0 +1,38 @@
+# Cursor Integration
+
+Converts all 61 Agency agents into Cursor `.mdc` rule files. Rules are
+**project-scoped** — install them from your project root.
+
+## Install
+
+```bash
+# Run from your project root
+cd /your/project
+/path/to/agency-agents/scripts/install.sh --tool cursor
+```
+
+This creates `.cursor/rules/<agent-slug>.mdc` files in your project.
+
+## Activate a Rule
+
+In Cursor, reference an agent in your prompt:
+
+```
+@frontend-developer Review this React component for performance issues.
+```
+
+Or enable a rule as always-on by editing its frontmatter:
+
+```yaml
+---
+description: Expert frontend developer...
+globs: "**/*.tsx,**/*.ts"
+alwaysApply: true
+---
+```
+
+## Regenerate
+
+```bash
+./scripts/convert.sh --tool cursor
+```