chore: configure renovate (extend local>CopilotKit/renovate)

[jpr5]

Migrates this repo's Renovate configuration to extend the org-wide central config at https://github.com/CopilotKit/renovate.

Phase 1 of the migration (Notion plan) scopes Renovate to the github-actions ecosystem only; npm/pip remain on Dependabot.

Red-Green Proof

Known bug: renovate.json was committed with 4-space indentation and failed prettier --check (CI format:check).

RED — before fix (npx prettier --check renovate.json):

Checking formatting...
[warn] renovate.json
[warn] Code style issues found in the above file. Run Prettier with --write to fix.
EXIT=1

FIX — npx prettier --write renovate.json (4-space → 2-space indent):

 {
-    "$schema": "https://docs.renovatebot.com/renovate-schema.json",
-    "extends": ["local>CopilotKit/renovate"]
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": ["local>CopilotKit/renovate"]
 }

GREEN — after fix (npx prettier --check renovate.json):

Checking formatting...
All matched files use Prettier code style!
EXIT=0

Full CI command npm run format:check (prettier --check .) also passes:

Checking formatting...
All matched files use Prettier code style!

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	42.44%	7169 / 16891
🔵	Statements	41.84%	7602 / 18165
🔵	Functions	40.14%	1273 / 3171
🔵	Branches	41.03%	4803 / 11706

Generated in workflow #33 for commit ab5bdc6 by the Vitest Coverage Report Action