docs: add Building Apps landing page intros, expand Strong Consistency, use Master-Detail Layout for form drawers

[peholmst]

Closes #6292. This is the second batch. The first one was #6320, and #6321 added the error-handling guide.

Section landing pages

Seven Building Apps section landing pages had front matter but no content: UI Basics, Views & Navigation, Forms & Data, Business Logic, Security, Integration, and Components. Each now has a short introduction, where to start, links to related sections, and a == Topics outline. This follows the pattern of the Testing and React Views pages.

Front matter fixes on these pages:

• Forms & Data and Add a Form: removed the promise of forms "using both Flow and Hilla". This covers that bullet in Building Apps: inconsistent Hilla/React terminology, Lumo/Aura token usage, and badges #6293.
• Integration: the section has a single page, on exposing a REST API, so the page title, description, and meta-description now say that instead of "integrate with other systems". The intro says that calls to other systems belong in application services.
• Security: the intro links the OAuth2 reference page, which Add Login doesn't link (Improve Getting Started and Building Apps for enterprise architecture evaluation #6288, finding 4). It also links both security-testing pages.
• Meta-descriptions are now 150–160 characters. The Components meta-description is still 126, as before; I didn't change it.

Strong Consistency

Replaced the stub and its TODO ("monoliths and self-contained systems") with four sections:

• Transactions, and how application services define them
• Where Strong Consistency Ends: a monolith or self-contained system can use one local transaction, while microservices can't, which leads to Eventual Consistency
• Concurrent Updates: lost updates, optimistic locking, and pessimistic locking
• Stale Data in the User Interface: strong consistency doesn't refresh views that are already open; server push does

Dialogs & Drawers

The drawer section had a TODO saying "Write about the new master-detail layout" and built the drawer by hand. It used setVisible() and LumoUtility classes. It now uses MasterDetailLayout:

• The view extends MasterDetailLayout. It calls setDetail(drawer) when a proposal is selected and setDetail(null) when the selection is cleared.
• The backdrop-click and Escape listeners clear the selection when the drawer is shown as an overlay.
• It links to the Add a Master-Detail View guide.
• It removes the LumoUtility styling (part of Building Apps: inconsistent Hilla/React terminology, Lumo/Aura token usage, and badges #6293).
• It fixes setAriaLabeledBy, which doesn't exist, to setAriaLabelledBy.

The example uses only MasterDetailLayout API that is available from 25.0. setDetailPlaceholder() (25.2) is avoided, so no since badge is needed.

Checks

• Compiled ProposalDrawer and ProposalView, extracted from the page, with javac -Xlint:deprecation against this repo's dependency classpath. The only stubs were Proposal, ProposalForm, and ProposalService. There were no errors or warnings.
• All 52 added xrefs and anchors resolve.
• Vale reports nothing on the changed lines.
• No pages moved or removed, so no redirects are needed.

After this PR, the only // TODO left in Building Apps and Getting Started is the one in add-login.adoc. It's a placeholder inside the code sample for the reader to fill in, so it stays.

🤖 Generated with Claude Code

[github-actions]

Preview Deployment

This PR has been deployed for preview.

URL: https://docs-preview-pr-6330.fly.dev

Changed pages

Added content is highlighted in green; removed content is marked in red on each page.

• building-apps/business-logic — modified, +15/-1 lines
• building-apps/components — modified, +16/-0 lines
• building-apps/forms-data — modified, +15/-1 lines
• building-apps/forms-data/add-form — modified, +1/-1 lines
• building-apps/forms-data/add-form/dialogs-and-drawers — modified, +18/-22 lines, 8 removal marker(s)
• building-apps/forms-data/consistency/strong — modified, +28/-6 lines, 2 removal marker(s)
• building-apps/integration — modified, +17/-3 lines, 1 removal marker(s)
• building-apps/security — modified, +17/-2 lines
• building-apps/ui-basics — modified, +13/-0 lines
• building-apps/views — modified, +15/-1 lines

Built from d35934d