fix(appkit): allow database initialization without arguments

[ditadi]

Summary

Allow database() and database({}) to initialize without explicit configuration.

• Load the named schema export from config/database/schema.ts; ship a valid empty starter in newly scaffolded apps.
• Resolve the PostgreSQL username from the application's Databricks credentials when PGUSER and DATABRICKS_CLIENT_ID are absent, using the same client for identity lookup and pool authentication.
• Preserve explicit overrides and validate the schema before pool creation.
• Check the packaged template's database starter before uploading the PR artifact.

Validation

• 4,983 tests passed, 1 skipped; build, docs, lint and typecheck passed.
• Created a fresh app with the actual Databricks CLI and prepared SDK tarballs.
• Started the unmodified generated server and received HTTP 200.
• Initialized database() and queried real local PostgreSQL without PGUSER or DATABRICKS_CLIENT_ID; the workspace identity/credential API was a local test double, not a live Lakebase workspace.

[github-actions]

📦 Bundle size report

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

@databricks/appkit

npm tarball (packed): 1.1 MB (+4.2 KB) — gzipped download (dist + bin; excludes release-only docs/NOTICE).

dist	raw	gzip
JS (runtime)	1.1 MB (+4.6 KB)	412 KB (+1.8 KB)
Type declarations	425 KB (+1.3 KB)	153 KB (+413 B)
Source maps	2.3 MB (+8.6 KB)	773 KB (+3.3 KB)
Other	11 KB	3.7 KB
Total	3.8 MB (+14 KB)	1.3 MB (+5.5 KB)

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

Entry	Initial (gz)	Lazy (gz)	Total (gz)	node_modules (min)	Own code (min)
.	95 KB (+8 B)	2.5 KB	98 KB (+8 B)	external	313 KB
./beta	93 KB (+729 B)	457 B	93 KB (+729 B)	external	279 KB (+2.0 KB)
./testing	17 KB (-1 B)	0 B	17 KB (-1 B)	external	52 KB
./tsdown	520 B	0 B	520 B	external	813 B
./type-generator	23 KB	0 B	23 KB	external	65 KB

Chunks:

Entry	Chunk	Load	Size (gz)
.	index.js	initial	91 KB
.	utils.js	initial	4.0 KB
.	remote-tunnel-manager.js	lazy	2.5 KB
./beta	beta.js	initial	76 KB
./beta	stream-manager.js	initial	5.8 KB
./beta	wide-event-emitter.js	initial	3.2 KB
./beta	databricks.js	initial	3.2 KB
./beta	configuration.js	initial	2.3 KB
./beta	service-context.js	initial	1.3 KB
./beta	client.js	initial	434 B
./beta	client-options.js	initial	220 B
./beta	supervisor-api.js	lazy	192 B
./beta	databricks.js	lazy	142 B
./beta	index.js	lazy	123 B
./testing	index.js	initial	17 KB
./tsdown	index.js	initial	520 B
./type-generator	index.js	initial	23 KB

@databricks/appkit-ui

npm tarball (packed): 350 KB (+4 B) — gzipped download (dist + bin; excludes release-only docs/NOTICE).

dist	raw	gzip
JS (runtime)	395 KB	132 KB
Type declarations	229 KB	84 KB (+1 B)
Source maps	766 KB	253 KB
CSS	16 KB	3.2 KB
Total	1.4 MB	473 KB (+1 B)

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

Entry	Initial (gz)	Lazy (gz)	Total (gz)	node_modules (min)	Own code (min)
./js	5.3 KB	49 KB	55 KB	208 KB	14 KB
./js/beta	20 B	0 B	20 B	0 B	0 B
./react	432 KB	49 KB	481 KB	1.3 MB	177 KB
./react/beta	1.0 KB	0 B	1.0 KB	0 B	1.9 KB

Chunks:

Entry	Chunk	Load	Size (gz)
./js	index.js	initial	5.2 KB
./js	chunk	initial	120 B
./js	apache-arrow	lazy	49 KB
./js/beta	beta.js	initial	20 B
./react	index.js	initial	430 KB
./react	tslib	initial	2.1 KB
./react	apache-arrow	lazy	49 KB
./react/beta	beta.js	initial	1.0 KB

[github-actions]

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📦 Try this PR's app template

Scaffolds a new app from this PR's SDK build. Run it in any folder (requires the GitHub CLI — gh auth login — and the Databricks CLI):

gh run download 34626747579 -R databricks/appkit -n appkit-template-0.74.1-pr.e83879e-fix-database-init-582 -D appkit-pr-582 \
  && unzip -o "appkit-pr-582/appkit-template-0.74.1-pr.e83879e-fix-database-init-582.zip" -d "appkit-pr-582" \
  && databricks apps init --template "appkit-pr-582"

The template pins @databricks/appkit and @databricks/appkit-ui to tarballs built from this branch, so the scaffolded app runs against this PR's code.