feat(lakebase): support CJS consumers and validate exports via attw

[MarioCadenas]

Closes #404.

• Build @databricks/lakebase as dual ESM + CJS via tsdown, emitting .js/.d.ts and .cjs/.d.cts artifacts. Update package.json exports with conditional import/require entries; the development condition is preserved for source consumers.
• Enable tsdown's built-in attw integration in @databricks/lakebase, @databricks/appkit, and @databricks/appkit-ui so type-resolution correctness across node10, node16, and bundler is validated on every build (level: error). appkit and appkit-ui use the esm-only profile; lakebase uses strict.

[github-actions]

📦 Bundle size report

Compared against bundle-size-baseline.json (main).

✅ No size changes vs the baseline.

@databricks/appkit

npm tarball (packed): 658 KB — gzipped download (dist + bin; excludes release-only docs/NOTICE).

dist	raw	gzip
JS (runtime)	686 KB	240 KB
Type declarations	268 KB	91 KB
Source maps	1.3 MB	445 KB
Other	11 KB	3.7 KB
Total	2.3 MB	779 KB

Per-entry composition (own code — deps external (as shipped))

Entry	Initial (gz)	Lazy (gz)	Total (gz)	node_modules (min)	Own code (min)
.	74 KB	2.5 KB	76 KB	external	243 KB
./beta	39 KB	231 B	39 KB	external	117 KB
./type-generator	18 KB	0 B	18 KB	external	53 KB

Chunks:

Entry	Chunk	Load	Size (gz)
.	index.js	initial	70 KB
.	utils.js	initial	4.0 KB
.	remote-tunnel-manager.js	lazy	2.5 KB
./beta	beta.js	initial	30 KB
./beta	databricks.js	initial	5.7 KB
./beta	service-context.js	initial	3.1 KB
./beta	client-options.js	initial	220 B
./beta	databricks.js	lazy	128 B
./beta	index.js	lazy	103 B
./type-generator	index.js	initial	18 KB

@databricks/appkit-ui

npm tarball (packed): 298 KB — gzipped download (dist + bin; excludes release-only docs/NOTICE).

dist	raw	gzip
JS (runtime)	354 KB	117 KB
Type declarations	204 KB	73 KB
Source maps	676 KB	220 KB
CSS	16 KB	3.3 KB
Total	1.2 MB	413 KB

Per-entry composition (consumer bundle — deps bundled, peerDeps external)

Entry	Initial (gz)	Lazy (gz)	Total (gz)	node_modules (min)	Own code (min)
./js	4.2 KB	49 KB	54 KB	208 KB	11 KB
./js/beta	20 B	0 B	20 B	0 B	0 B
./react	429 KB	49 KB	477 KB	1.3 MB	166 KB
./react/beta	20 B	0 B	20 B	0 B	0 B

Chunks:

Entry	Chunk	Load	Size (gz)
./js	index.js	initial	4.1 KB
./js	chunk	initial	120 B
./js	apache-arrow	lazy	49 KB
./js/beta	beta.js	initial	20 B
./react	index.js	initial	427 KB
./react	tslib	initial	2.1 KB
./react	apache-arrow	lazy	49 KB
./react/beta	beta.js	initial	20 B