docs: add search dev-mode limitation to docs README

[Copilot]

Multi-device docs testing surfaced that the Astro/Starlight search is silently unavailable in dev mode — contributors running npm run dev see a dead search button with no documented explanation.

Changes

• docs/README.md: Added ### Search not available in dev mode under the existing ⚠️ Known Dev-Mode Limitations section, matching the style of the existing sitemap limitation entry. Documents the expected dev-mode message and directs contributors to npm run build && npm run preview to test search locally.

[github-actions]

Hey @Copilot 👋 — thanks for documenting the Astro/Starlight search dev-mode limitation! That's exactly the kind of contributor-friendly note that saves people debugging time. A couple of things worth tidying up before this lands:

• Unfocused diff — the PR description mentions only a single change to docs/README.md, but the diff spans 187 files — almost entirely .github/workflows/*.lock.yml files. These lock-file updates appear to have been swept in from the branch state rather than being intentional parts of this fix. The docs/README.md change should be isolated in its own clean commit/PR so reviewers can confirm the intent quickly.
• No tests — for a docs-only change this is low-risk, but if any automated spell-check or link-check CI exists in this repo, make sure those pass on the trimmed branch.

If you'd like a hand cleaning this up, here's a ready-to-run agent prompt:

The PR branch `copilot/fix-multi-device-docs-testing-report` contains 187 changed files, but the only intentional change is adding a "Search not available in dev mode" note under the "Known Dev-Mode Limitations" section of `docs/README.md`.

Please:
1. Reset the branch to `main`.
2. Cherry-pick or re-apply only the `docs/README.md` change (add the `### Search not available in dev mode` subsection matching the style of the existing sitemap limitation entry, directing contributors to `npm run build && npm run preview`).
3. Commit with message: `docs: document search unavailability in dev mode`
4. Force-push the cleaned branch so the PR diff shows only the intended single-file change.

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[pelikhan]

@copilot merge main and recompile