CodeMirror stack 1/4: upgrade to latest 6.x, fix sql() option names, rollup build

[asg017]

Part 1 of the CodeMirror stack (integration view: #2833). Pure maintenance — no behavior change beyond a fresher editor.

What

• Upgrade to current CodeMirror 6.x: codemirror 6.0.1 → 6.0.2, @codemirror/lang-sql 6.3.3 → 6.10.0, transitives refreshed (autocomplete 6.20.3, view 6.43.6, state 6.7.1). Everything is still major-version 6 — no breaking changes; no CodeMirror 7 exists.
• Fixes a long-standing silent bug: sql() was called with defaultTableName / defaultSchemaName, which have never been valid lang-sql options (the real names are defaultTable / defaultSchema). They were silently ignored — nothing supplied them, but part 2 of the stack makes defaultTable load-bearing.
• caseInsensitiveIdentifiers: true on the curated SQLite dialect (lang-sql ≥ 6.7): stops completions auto-quoting mixed-case identifiers.
• Version-agnostic filenames: cm-editor-6.0.1.{js,bundle.js} → cm-editor.{js,bundle.js} (git records clean renames), so upgrades no longer require editing a template. Cache busting was already handled by the static() template helper's ?_hash= content hash.
• Real build config: rollup.config.mjs + npm run build:codemirror replace the six-flag one-liner previously documented in docs/contributing.rst; docs rewritten accordingly.

Review notes

• The bundle diff is a rebuild — reproduce with npm install && npm run build:codemirror (byte-identical output).
• The curated keyword list from Upgrade to CodeMirror 6, add SQL autocomplete #1893 is intentionally kept over lang-sql's stock SQLite dialect.

Testing

Full pytest suite green. Manual QA: editor mounts on /fixtures, completion popup, Shift/Meta-Enter submit, Format SQL, resize handle.

The stack

#	PR	Content
1/4	#2834	CM 6.x upgrade, option-name bugfix, rollup build
2/4	#2835	Rich schema autocomplete, /-/editor-schema.json, defaultTable
3/4	#2836	datasette-sql-editor ESM primitives
4/4	#2837	<datasette-sql-editor> element + core-page dogfood

Each PR is based on the previous branch; merge top-down, retargeting the next base to main as each lands. Bundle files (*.bundle.js) conflict on rebase by nature — resolve by re-running npm run build:codemirror, never by merging. Integration view of the whole branch: #2833.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (db82123) to head (28d8113).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2834   +/-   ##
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  Coverage   0.00%   0.00%           
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  Files         73      73           
  Lines      12208   12208           
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  Misses     12208   12208           

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