fix(frontend): make breadcrumb links fill the header row

[posthog-eu]

Summary

The breadcrumb header renders on every app page as a 64px-tall bar, but only the small crumb text was clickable — the crumbs were bare inline <router-link>s (px-1, no vertical padding) sitting in an h-16 row, leaving most of the bar as dead space that looks like navigation. A second target was dead by construction: the last crumb linked to the route you're already on, so that click could never do anything.

• Who it hurts: 375 dead clicks landing on the bare breadcrumb container across 282 sessions and 201 distinct users over 60 days. Nothing is blocked — users route around it — but it's continuous "is this broken?" friction on every app page.
• Root cause is one row up from where the original signal pointed. The "Bundles" tab itself works fine; the failure is the breadcrumb bar above it.

Test plan

1. Open any app page (e.g. /app/<app>/bundles) on desktop (lg breakpoint).
2. Hover the breadcrumb bar — parent crumbs now read as links (persistent underline) before you interact.
3. Click anywhere in the full height of a parent crumb (not just the text baseline) — navigation fires.
4. Confirm the final crumb is plain text with no link/pointer and no navigation on click.

Verification scope: change is a deterministic Tailwind layout adjustment; eslint and vue-tsc are clean for Navbar.vue. A live session reproduction wasn't run — the app page requires backend auth not available in this environment.

Screenshots

Mechanism:

Before	After
Crumb = <router-link px-1 text-sm> — hit target ≈ text height, thin strip centered in a 64px bar	Crumb = flex items-center h-16 px-2 — hit target fills the full row height
Last crumb is a <router-link> to the current route → dead click	Last crumb is a plain <span aria-current="page"> → no dead target
hover:underline only — no affordance until you try	Persistent underline so crumbs read as links up front

Checklist

• My code follows the code style of this project and passes
  bun run lint:backend && bun run lint.
• My change requires a change to the documentation.
• I have updated the documentation
  accordingly.
• My change has adequate E2E test coverage.
• I have tested my code manually, and I have provided steps how to reproduce
  my tests

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud