fix(astro): require Astro 6 peer dep (>=6 <7)

[MajorTal]

Problem

@run402/astro's SSR runtime (astro/src/runtime/server.ts) does await import("astro/app/entrypoint") — an Astro-6-only export. Registry-confirmed: astro@5.18.2 exports only ./app and ./app/node; ./app/entrypoint first appears in Astro 6.

But peerDependencies.astro was >=5 <7. A consumer on Astro 5 using the default export default run402() preset (or createRun402Adapter()) therefore aborted during astro build's "Building server entrypoints" step with the opaque:

[commonjs--resolver] Missing "./app/entrypoint" specifier in "astro" package

The try/catch in getAstroApp() doesn't help — Vite resolves the specifier at bundle time, before the runtime guard runs.

Fix

Tighten the peer range to >=6 <7 so the declared support matches what the SSR adapter actually requires — npm now warns at install time instead of crashing mid-build.

• astro/package.json — astro: ">=5 <7" → ">=6 <7"
• package-lock.json — reconciled recorded peer range
• astro/README.md — install note "Astro 5 or 6" → "Astro 6" + runtime/image-only nuance
• astro/CHANGELOG.md — dedicated Fixed entry; corrected the now-contradictory "peer range unchanged" line in the @run402/astro: createRun402Adapter incompatible with astro@6 — NoAdapterInstalled despite registration #403 entry

The build-time image integration (run402Image() / the named run402 alias, used without the SSR adapter) never bundles runtime/server.ts and still runs on Astro 5, but Astro 5 is now outside the supported peer range.

Verification

build:core + build:sdk → tsc --noEmit -p astro ✅ → npm test --workspace=astro (285 pass, 0 fail) ✅ → npm run build --workspace=astro ✅.

Notes

• This fixes the repo; consumers only get it after a new @run402/astro is published (separate, authorized step — not done here).
• Sibling private-repo drift (the packages/astro/ copy + the live run402.com/errors/ page still advising "pin Astro ^5") is tracked in kychee-com/run402-private#469.

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