Unify create/import into single Add Wallet view

Merge "Create new wallet" and "Import recovery phrase" into one
"Add wallet" screen. The recovery phrase textarea starts empty.
A clickable die button generates a random phrase and shows a
backup warning. Users who already have a phrase just paste it.
Welcome screen simplified to two options: "Add wallet" and
"Import private key". README updated to match.

README.md

@@ -145,31 +145,31 @@ The popup has the following views, switched via simple show/hide:
 
 1. **Lock**: Password input + Unlock button. Shown when the wallet is locked or
    on first open after browser restart.
-2. **Welcome**: Shown on first use. Three options: "Create a new wallet", "I
-   have a recovery phrase", "I have a private key". Password is set during this
-   first flow.
-3. **Create**: Displays a generated 12-word recovery phrase with instructions to
-   write it down. User sets a password and confirms.
-4. **Import recovery phrase**: Paste a 12 or 24 word recovery phrase. Password
-   fields shown only on first use.
-5. **Import private key**: Paste a private key. Password fields shown only on
-   first use.
-6. **Main**: All wallets listed, each showing its addresses with truncated
-   address and ETH balance. "+" next to HD wallets to add another address. "+
-   Add wallet" at the bottom. Settings and Lock buttons in the header. Future: a
-   sub-heading showing total portfolio value in USD (and eventually other
-   currencies).
-7. **Add wallet**: Choose wallet type (new, recovery phrase, private key) — same
-   three options as Welcome but without password setup.
-8. **Address detail**: Full address (click to copy), ETH balance, USD value
+2. **Welcome**: Shown on first use. Two options: "Add wallet" (recovery phrase
+   based) and "Import private key". Password is set during the first wallet
+   addition.
+3. **Add wallet**: A unified view for both creating and importing recovery
+   phrase wallets. The recovery phrase text area starts empty. A clickable die
+   button `[die]` generates a random 12-word phrase and fills it in. If the user
+   already has a phrase, they paste it directly. When the die is clicked, a
+   warning box appears reminding the user to write the phrase down. Password
+   fields are shown only on first use.
+4. **Import private key**: Paste a private key. This creates a wallet with a
+   single address. Password fields shown only on first use.
+5. **Main**: All wallets listed, each showing its addresses with truncated
+   address and ETH balance. "+" next to recovery phrase wallets to add another
+   address. "+ Add wallet" and "+ Import private key" buttons at the bottom.
+   Settings and Lock buttons in the header. Future: a sub-heading showing total
+   portfolio value in USD (and eventually other currencies).
+6. **Address detail**: Full address (click to copy), ETH balance, USD value
    (future), Send/Receive buttons, token list with "+ Add" button.
-9. **Send**: Token selector, recipient address, amount. Cancel returns to
+7. **Send**: Token selector, recipient address, amount. Cancel returns to
    address detail.
-10. **Receive**: Full address displayed with "Copy address" button.
-11. **Add token**: Enter contract address. The extension looks up the token
-    name/symbol automatically.
-12. **Settings**: Network (RPC endpoint URL) with explanatory text.
-13. **Approval**: When a website requests wallet access or a signature, shows
+8. **Receive**: Full address displayed with "Copy address" button.
+9. **Add token**: Enter contract address. The extension looks up the token
+   name/symbol automatically.
+10. **Settings**: Network (RPC endpoint URL) with explanatory text.
+11. **Approval**: When a website requests wallet access or a signature, shows
     the site origin, request details, and Allow/Deny buttons.
 
 ### External Services