fix(theme): restore the navigation landmark, the single h1 and the result URL contrast

[marevol]

Why

The bootstrap static theme is now the default search UI. Compared with the JSP search pages it regressed on three accessibility points:

• No navigation landmark. The header <nav> carried role="banner", which replaces its implicit navigation role, so the accessibility tree of the top page had no navigation landmark.
• Two <h1> on the top page. The visually-hidden page heading and the logo heading (h1.mainLogo) were both exposed.
• Result URL contrast below WCAG AA. The result URL (#result .site cite) was #009933, 3.75:1 on white. The JSP page used #00852c, 4.78:1.

What changes

• index.html: drop role="banner" from the header <nav>; the enclosing <header> is the banner.
• index.html / app.js: the page heading gets id="page-heading", and showView() hides it on the home view, whose logo heading is the page's h1, as on index.jsp. Every other view keeps the page heading as its only h1.
• styles.css: the result URL uses #00852c.
• BundledBootstrapThemeTest checks the nav role, the heading id and the cite contrast (the contrast test fails on main); app.test.js checks the heading is hidden on the home view only.

The theme version stays 1.3.0: it was set for 15.9 and has not been released yet.

Verification

• mvn test -Dtest=BundledBootstrapThemeTest: 127 tests passed.
• Theme JS tests (src/test/js, npx vitest run): 572 passed.
• Headless Chromium against a distribution built with this change, OpenSearch 3.8, reading the accessibility tree and computed styles, before (main) → after:

Check	Before	After
Landmarks, top page	banner, main, search, contentinfo	banner, navigation, main, search, contentinfo
Landmarks, results page	banner, search, main, complementary, navigation (pagination), contentinfo	banner, navigation, search, main, complementary, contentinfo
h1 in the accessibility tree, top page	2 (Fess Search ×2)	1
h1, results page	1	1
Result URL colour / contrast	#009933, 3.75:1	#00852c, 4.78:1