Global server selector panel

[t1]

Parent: #13 (Multi-server support)

Generate the server selector panel inline in index.html with radio buttons for the spec's top-level servers array (non-template servers only — template variables are #38).

Scope

Header display:

• Resolved server URL shown inline in the header bar, between page title and mode toggle
• Always a clickable toggle (▶/▼) that expands/collapses the server panel
• Even with a single server, the toggle is active (users can add custom URLs in Global server selector panel #39)

Server panel (collapsible):

• Radio button for each global server, labeled with the URL
• Server description shown next to the URL (if defined in the spec)
• If the spec defines no servers field, a single entry shows the resolved origin URL (resolved client-side in JS)
• Empty #server-override placeholder slot (used by Template server variables and presets #40)

JS:

• Expand/collapse toggle (following globalHeaders pattern with is-collapsed class)
• On radio selection, update data-base-url on the mode toggle element
• Persist selected server in localStorage (openapi-ui-server)
• Restore selection on page load

CSS:

• Follow globalHeaders panel styling pattern

Design spec

See docs/superpowers/specs/2026-04-11-issue-13-multi-server-support-design.md

[t1]

Agent: starting work

Type: Feature
Summary: Add global server selector panel inline in index.html with radio buttons for each server, collapsible toggle, localStorage persistence, and base URL update on selection. This is the foundation for the multi-server support feature.
Design decisions:

• Server URL displayed inline in header bar (between title and mode toggle)
• Panel follows globalHeaders pattern for styling and expand/collapse behavior
• Even single-server specs get the toggle (users can add custom URLs in future sub-issues)
• If no servers defined, resolve origin URL client-side
  Acceptance criteria:
• Radio button for each global server with URL label and description
• Expand/collapse toggle with is-collapsed class
• Selection persisted in localStorage (openapi-ui-server)
• data-base-url attribute updated on mode toggle element
• Empty #server-override slot for operation-level overrides
  Files: core/src/main/java/com/github/t1/openapiui/IndexPage.java, core/src/main/resources/openapi-ui.css, core/src/main/resources/openapi-ui.js, core/src/test/java/com/github/t1/openapiui/BrowserTest.java

[t1]

Agent: done

Commit: b7525ad
Summary: Implemented global server selector panel with collapsible UI following the globalHeaders pattern. Panel displays radio buttons for each global server with URLs and descriptions, persists the selected server to localStorage (openapi-ui-server key), and updates the data-base-url attribute on the mode toggle element. Added empty #server-override slot placeholder for future per-operation server overrides. Demo app updated to showcase multiple servers.
Tests: Added 8 comprehensive tests covering panel presence, radio button generation, labels, descriptions, default selection, toggle behavior, collapse state, and override slot presence. All 413 tests in the core module pass.
CI: passed