fix(ui): make Terminology navigation configuration-aware

[Gordex2014]

What changed

• Replace the inert Terminology sidebar placeholder with a native link driven by HFS_TERMINOLOGY_SERVER.
• Open a valid configured URL in a new tab with noopener, noreferrer, and htmx boosting disabled.
• Add /ui/terminology for missing and invalid configuration states.
• Reuse the setup panel from Resources for configuration instructions and errors.
• Add the new UI copy in English, Spanish, and German.
• Register the new page in the shared e2e route list.

Configuration behavior

HFS_TERMINOLOGY_SERVER	Behavior
Valid	Opens the exact configured URL in a new tab.
Invalid	Opens /ui/terminology and explains the URL requirements.
Unset	Opens /ui/terminology and shows how to configure the variable.

A valid destination must be an absolute HTTP or HTTPS URL with a host. Paths and a trailing slash are allowed. Credentials, query strings, fragments, surrounding whitespace, and other schemes are rejected for navigation.

Invalid values never reach an href or appear in the rendered page.

Accessibility and progressive enhancement

Both navigation paths use native anchors, so they remain focusable and keyboard-activatable without JavaScript.

The external link:

• Announces that it opens in a new tab.
• Uses target="_blank" and rel="noopener noreferrer".
• Uses hx-boost="false" to preserve native browser navigation.

Scope

This change does not add a terminology browser or administrative console. That work remains tracked by #551.

It does not change how search, validation, FHIRPath, or editor pickers consume the configured terminology server.

Verification

• cargo fmt --all -- --check
• cargo test -p helios-ui --test router_http terminology_navigation_reflects_the_configuration
• cargo test -p helios-ui catalogs_share_the_same_key_set
• cargo clippy -p helios-ui --all-targets --no-deps -- -A clippy::question_mark -D warnings
• Manual QA with valid, invalid, and unset configurations
• Keyboard and no-JavaScript navigation

Closes #611

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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