feat(PLT-3073): forward Engine events to localhost

[TheMostlyGreat]

Outcome

Adds arcade event listen --forward-to http://localhost:<port>/<path> so developers can exercise the production event envelope locally without exposing their machine.

What changes

• reads the authenticated project event feed introduced by ArcadeAI/monorepo#3742
• defaults org/project from active CLI context and supports server-side selectors
• signs each forward with a one-session Standard Webhooks secret and stable event ID
• refreshes CLI authorization before each poll so long-running sessions survive token rotation
• retries ambiguous failures in order; permanent local receiver rejection stops with an actionable URL/signing-secret error
• permits only explicit loopback hosts, re-resolves every attempt, disables environment proxies and redirects
• includes a minimal verifying and deduplicating receiver

Verification

• 42 focused event-listener and receiver tests pass
• 3,775 full-suite tests pass; 1 skipped
• focused Ruff and mypy: clean
• source and wheel build: green
• real Engine → feed → CLI → signed receiver proof: passed

Merge gate

Ready for review. Merge remains intentionally gated until ArcadeAI/monorepo#3742 is available in the selected Engine release.

Linear: https://linear.app/arcadedev/issue/PLT-3073

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[codecov]

Codecov Report

❌ Patch coverage is 90.05525% with 18 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
libs/arcade-cli/arcade_cli/event.py	89.94%	18 Missing ⚠️

Files with missing lines	Coverage Δ
libs/arcade-cli/arcade_cli/main.py	33.55% <100.00%> (+1.11%)	⬆️
libs/arcade-cli/arcade_cli/event.py	89.94% <89.94%> (ø)

... and 1 file with indirect coverage changes

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[cursor]

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[evantahler]

…. no event system is on main yet

[github-actions]

This pull request has been automatically marked as stale because it has had no activity for 14 days. It will be closed in 14 days if no further activity occurs. If this is still relevant, please leave a comment or remove the stale label.