fix: polish dashboard connection flows

[ankitranjan7]

Motivation

Fix several dashboard UI bugs around provider/connection navigation, named connection creation, secret display, stale connection filters, logout redirects, and missing routes.

What Changed

• Reused the provider catalog named-connection flow on provider detail pages when a default connection already exists.
• Made provider summaries and connection rows clickable, while preserving row actions.
• Removed the Vault nav/page and added a concise custom missing-page view for broken routes.
• Synced the connections page provider filter to the URL so returning to /connections shows all connections again.
• Added clearer primary back buttons on provider and connection detail pages.
• Redacted provider configuration secrets and connection secrets by default with reveal controls.
• Redirected connection-detail logout back to /connections after the logout completes.

Verification

• uv pip install -e ".[dev]"
• uv run pnpm --dir ui lint
• ./scripts/build-ui.sh
• uv run ruff check src/ tests/
• uv run ty check src/
• uv run pytest
• uv run ruff check --fix src/ tests/
• uv run ruff format src/ tests/
• uv run --with pre-commit pre-commit run --all-files
• Browser smoke check: /vault renders the new custom missing-page card; /connections route resolves under local dev server.