Pin remaining drizzle-kit and drizzle-seed install commands to @rc

[dankochetov]

Summary

Pins the remaining untagged install commands to the @rc dist-tag for the 1.0 release-candidate window: -D drizzle-kit -> -D drizzle-kit@rc in the six kit-overview.mdx pages, and drizzle-seed -> drizzle-seed@rc in the six seed-overview.mdx pages (one dialect each: cockroach, mssql, mysql, pg, singlestore, sqlite). Everything else on main was already @rc-pinned.

Flags for maintainers

• Validator companions have no rc tag. drizzle-zod, drizzle-valibot, drizzle-typebox, drizzle-arktype currently have no rc dist-tag published (their newest v1-line snapshot is a 1.0.0-beta.14 prerelease), so their install commands were deliberately left untagged in this PR. Publishing rc tags for these packages would let a follow-up sweep pin them too.
• graphql.mdx pairing left as-is. That page pins drizzle-orm@latest next to drizzle-graphql (latest 0.8.5, no rc tag, v1 compatibility with drizzle-graphql is unknown). Left untouched on purpose rather than guessing at a pairing that might not work.
• No llms.txt change needed. It's generated from the content collection at build time (src/pages/llms.txt.ts), so it picks up these fixes automatically once this merges and deploys.

Test plan

• git grep -n '<Npm>drizzle-seed</Npm>' -- src/content returns nothing
• git grep -nE '^ -D drizzle-kit$' -- src/content returns nothing
• git grep -nE 'drizzle-(kit|orm|seed)@beta' -- src/content ':!*latest-releases*' returns nothing
• git diff origin/main --stat touches only the 12 intended files

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