guides: lead the index with the Agent Skills card

[leoncheng57]

Closes #255

What

Moves the inlined Agent Skills <article> in GuidesIndexRoute.tsx from the bottom of the guide list to the top, so it is the first card on /guides.

PR #241 put it last on the reasoning that the one off-site entry belongs below the first-party pages. That's now overridden — it's the newest work and should be the most prominent.

The comment

The card now sits above {guides.map(...)}, i.e. above content sorted by updatedAt descending. That reads like a sorting bug at a glance, so the block carries a comment saying the placement is deliberate and pointing at both issues. Without it someone eventually "fixes" it back.

Tests

guides-route.test.tsx had no ordering assertions, so a silent re-sort would not have been caught. Added one:

• leads the index with the agent skills card, ahead of the date-sorted guides — collects the sibling <article> cards and asserts the Agent Skills card is index 0 and the manager/worker markdown guide lands after it. Verified it is not vacuous: flipping the expectation to last-position makes it fail.

No existing test needed changing. Both GitHub ↗ lookups were already scoped to their own <article> (the OpenCode Remote Control one since #241), so the duplicate match stays resolved after the reorder. The getAllByRole('link', { name: /read guide/ })[0] query is also unaffected — the Agent Skills CTA is browse skills ↗, not read guide.

Verification

Node 26.3.0.

	baseline (origin/main)	this branch
npm run test:run	35 failed / 403 passed (438)	35 failed / 404 passed (439)
failing files	weather-routes.test.tsx only	weather-routes.test.tsx only

Identical failure set; the delta is the one new passing test. Those 35 are the known pre-existing Node 26 breakage — Node emits its own localStorage that shadows jsdom's, so window.localStorage.clear() in that file's beforeEach throws. Reproduced on clean origin/main first and left alone.

• npm run lint — clean
• npm run build — succeeds

Build output is not committed, matching main (docs/ was last touched in #204, not per-change).

Visual

Served the production build and read back the rendered card order on /guides:

0. $ Agent Skills
1. $ Building a Custom Coding-Agent IDE with OpenHands
2. $ Running Parallel Coding Agents with a Manager and Workers
3. $ cmux personal config
4. $ opencode personal config
5. $ OpenCode Remote Control BETA