test: add Playwright UI regression tests for dashboard pages

[coopernetes]

Background

PR #246 fixed several UI regressions that were introduced across multiple commits and only caught by manual inspection:

• URL Rules page showing every rule as "any: *" (wrong field names after 34aebb9 backend refactor)
• Admin connectivity panel crashing with TypeError when tls/http fields were absent (NON_NULL Jackson config strips nulls)
• All provider dropdowns showing hostname instead of friendly name throughout the UI
• scanDiff step content showing branch ref instead of blocked pattern/file

None of these were caught by CI because we had no Playwright tests for these pages. We do have Playwright tests for the push detail and permissions flows (added in #243) but nothing covering the Repos, Admin, or rule/permission management pages.

Scope

Add Playwright e2e tests covering at minimum:

• Repos → Rules tab: rules load and display target/value/matchType correctly; Add Rule modal submits target/value/matchType to the API (not old slug/owner/name)
• Repos → Rules tab: provider dropdown shows friendly name not hostname
• Admin → Connectivity: page renders without crash when tls/http are absent in the response (mock an HTTP provider or TCP-fail scenario)
• Admin → Connectivity: page renders correctly for a successful HTTPS provider response
• Add Permission / Add SCM identity: provider dropdown shows friendly name
• Active repos: provider label shows friendly name; clone URL is constructed from proxyPath

Acceptance criteria

• Tests run in CI as part of the existing Playwright job
• A future backend field rename (like 34aebb9) that breaks the UI shape causes a CI failure rather than a silent regression reaching review