fix(routing): resolve direct/path-based deep links to hash routes

[Zhekinmaksim]

Closes #614.

The portal uses hash-based routing (svelte-spa-router), but several sidebar links render as plain path URLs (/testnets, /metrics, ...). When opened in a new tab, copied/shared, refreshed, or indexed, these arrive without a hash and resolve to a 404/NotFound.

Changes:

• Add src/lib/normalizePath.js: route-agnostic path-to-hash normalization. Unknown paths fall through to the router's own NotFound; static assets and server-handled prefixes (/api, /oauth, ...) are left untouched. Replaces the previous hardcoded two-prefix block in App.svelte.
• Sidebar.svelte: convert internal hrefs to hash form so copied/new-tab/indexed links are valid at the source.
• src/tests/normalizePath.test.js: unit coverage (11 tests).

Verified: new tests pass, npm run build succeeds, no new regressions in the existing suite.