Harmonise gitignore responsibility across writers (claude internalizes, cursor delegates to caller)

[byapparov]

Summary

Surfaced by review of #21 ([MINOR] in src/writers/claude.ts:182).

The two writer modules expose inconsistent contracts for managing .gitignore:

• installClaudePlugin (since fix: scope plugin enablement per project so multi-org developers get only their current repo's MCP + skills (#20) #21) calls ensureGitignore internally to add .claude/settings.local.json.
• installCursor delegates .cursor/mcp.json to its caller (main() in cli.ts, which builds a gitignoreEntries array and applies them at the end).

A future consumer calling installCursor directly outside of cli.ts would miss the gitignore step.

Why #21 kept the inconsistency

The self-contained approach in installClaudePlugin makes its gitignore contribution unit-testable in test/writers/claude.test.ts without spinning up the interactive CLI. Moving it back out to cli.ts would lose that test coverage. The principled fix is the opposite direction — move cursor's gitignore call into installCursor to match — but that touches installCursor and its tests, which is out of scope for #21's project-scope-enablement work.

Proposed fix

Move ensureGitignore(['.cursor/mcp.json']) into installCursor. Remove the corresponding push from cli.ts main(). Update test/writers/cursor.test.ts with an equivalent assertion to the one in claude.test.ts (adds .cursor/mcp.json to project .gitignore).

After this, cli.ts no longer needs the gitignoreEntries: string[] accumulator at all — each writer owns its own gitignore contributions.

Acceptance

• installCursor writes its .gitignore entry without help from the caller.
• cli.ts main() no longer references gitignoreEntries or calls ensureGitignore directly.
• Direct programmatic use of installCursor produces the same on-disk state as today via npx @aictrl/plugin.
• No behaviour change for installClaudePlugin.