docs(deployment): add mysql:// to environment-variables.mdx's OS_DATABASE_URL example list

[os-project-manager]

Fixes#9075

What

content/docs/deployment/environment-variables.mdx's OS_DATABASE_URL row
carries an e.g. example list of connection-string schemes. It named
file:./data.sqlite, postgres://…, mongodb://…, memory:// — omitting
mysql:// even though MySQL was ruled a supported deployment target
(#8739) and both detectDriverFromUrl (runtime) and inferDriverTypeFromUrl
(CLI) infer it via /^mysql2?:\/\//i.

Added mysql://… to the list, in the same one-scheme-per-target style the
row already uses for postgres:// (i.e. no mysql2:// alias spelled out).

Why this shape, and why it's small

Per the issue: this list is explicitly e.g., not a closed instruction like
self-hosting.mdx's OS_DATABASE_URL row (#9053 / PR #9076) — nothing on
the page was untrue before this change, only incomplete. So the fix is a
one-scheme addition, not a rewrite:

• No second caveat pointer added. The very next row,
  OS_DATABASE_DRIVER, already carries the MySQL dialect-caveat pointer PR
  docs(data-modeling): publish MySQL's two documented degradations as deployer-facing caveats #9052 landed on this page (Read [MySQL dialect caveats](/docs/data-modeling/drivers#mysql-dialect-caveats)…).
  A second pointer one row above it would be redundant, not helpful.
• mysql2:// intentionally left out, even though the runtime accepts
  it. self-hosting.mdx's equivalent row deliberately names one canonical
  scheme per target and never spells an alias (postgres:// not
  postgresql://, mongodb:// not mongodb+srv://). This page's e.g.
  list follows the same convention already (one scheme each for sqlite/
  postgres/mongodb), so mysql:// alone matches it; data-modeling/drivers.mdx's
  inference table remains the exhaustive alias reference for both
  mysql:// and mysql2://.

Out of scope

• No sweep of content/docs/** for further dialect-parity gaps — the MySQL's documented degradations are still source comments, not published support-matrix caveats — ruling item 2 of #8739 has no card #9029
  fence on that stands. Nothing else was found while making this edit.
• No source, config, or driver-behaviour change.
• content/docs/releases/** untouched.

Verification

At 657ef16fd (this branch's HEAD):

• pnpm check:docs-audit-scope — OK (178 hand-written docs in scope; 9
  release-owned pages review-only).
• pnpm check:docs-redirects — OK (92 redirect entries checked).
• pnpm check:role-word — OK (43 baselined files, no new occurrences).
• pnpm check:nul-bytes — OK (5973 files scanned, no raw control bytes).
• node scripts/pm/dispatch-gates.mjs content/docs/deployment/environment-variables.mdx
  named exactly these three families for the changed path; no anchors or
  page-path links were added, so check:doc-anchors / Check Documentation Links are not implicated by this diff.

Generated by Claude Code

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Generated by Claude Code