fix(connect): fix tailnet 'Connection Failed' (pasted-URL double scheme) + surface real error (#1)

* fix(connect): surface real connection error instead of generic dialog

testConnection swallowed the actual fetch error and returned a bare
boolean, so every failure collapsed to the same "Connection Failed"
text. On-device this made tailnet/LAN connect failures impossible to
diagnose (DNS vs timeout vs 401 vs cleartext all looked identical).

- testConnection now returns { ok, error } with the real error message
- add.tsx and [id].tsx dialogs show the error + target URL, plus a
  Tailscale/MagicDNS hint
- IP field keyboard: decimal-pad -> url, so tailnet hostnames can be
  typed (not just pasted)

Verified backend is healthy and reachable over tailnet (health 200,
port 4096 open in packet filter, cleartext present in shipped v0.2.0
APK), so the failure is client-side and was previously unobservable.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix(connect): normalize pasted IP/URL to avoid double scheme

Quick-connect blindly did `http://${ip}:${port}`. Pasting a full URL
(e.g. "http://100.108.64.76:4096", as the clipboard auto-paste offers)
produced "http://http://100.108.64.76:4096:4096" -> malformed URL ->
"Network request failed". This is the real tailnet connect failure:
typing a bare IP worked, pasting the displayed URL did not.

buildUrl now strips an existing http(s) scheme, drops any path, and
lifts a trailing :port out of the host field, so pasted full URLs,
host:port, and bare hosts all resolve to a single well-formed URL.

Reproduced and fixed on the Android emulator (paste full URL: fails
before, connects after).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/stores/connections.ts

@@ -30,7 +30,7 @@ interface ConnectionsState {
   addConnection: (connection: Omit<ServerConnection, "id">, password?: string) => Promise<void>
   removeConnection: (id: string) => Promise<void>
   setActiveConnection: (id: string) => Promise<void>
-  testConnection: (connection: ServerConnection, password?: string) => Promise<boolean>
+  testConnection: (connection: ServerConnection, password?: string) => Promise<{ ok: boolean; error?: string }>
   updateConnection: (id: string, updates: Partial<ServerConnection>) => Promise<void>
   refreshProject: () => Promise<void>
   // Create a one-off client pointing at a specific directory (for cross-project operations)
@@ -227,9 +227,9 @@ export const useConnections = create<ConnectionsState>((set, get) => ({
       })
 
       await client.global.health()
-      return true
-    } catch {
-      return false
+      return { ok: true }
+    } catch (error) {
+      return { ok: false, error: error instanceof Error ? error.message : String(error) }
     }
   },