fix(ui): add show/hide toggle for API key inputs and populate key on edit

Add eye toggle button for all API key input fields so users can verify their keys before saving.

Changes:

- BaseProviderForm: wrap single API key field (Gemini/Codex/Claude/Vertex) with passwordField + toggle button

- BaseProviderForm: wrap per-entry API key fields (OpenAI-compatible) with passwordField + toggle button

- BaseProviderForm: extract applyRawApiKey helper to populate apiKey from resource.raw in edit mode

- BaseProviderForm: sync initialFormSignature with applyRawApiKey to prevent false isDirty

- sharedForm.module.scss: add .passwordField, .passwordInput, .passwordToggle styles

- i18n: add showApiKey/hideApiKey keys to en, zh-CN, zh-TW, ru locale files

- accessibility: add aria-label and title attributes on both toggle buttons

src/features/providers/sheets/forms/sharedForm.module.scss

@@ -490,6 +490,64 @@
   }
 }
 
+.passwordField {
+  position: relative;
+  display: flex;
+  align-items: center;
+}
+
+.passwordInput {
+  width: 100%;
+  height: 36px;
+  padding: 8px 36px 8px 12px;
+  border-radius: var(--radius-md);
+  border: 1px solid var(--border-color);
+  background: var(--bg-primary);
+  color: var(--text-primary);
+  font-size: 13px;
+  font-family: inherit;
+  box-sizing: border-box;
+
+  &::placeholder {
+    color: var(--text-tertiary);
+  }
+
+  &:focus {
+    outline: none;
+    border-color: var(--primary-color);
+    box-shadow: 0 0 0 3px var(--primary-10);
+  }
+
+  &:disabled {
+    opacity: 0.6;
+    cursor: not-allowed;
+  }
+}
+
+.passwordToggle {
+  position: absolute;
+  right: 8px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 4px;
+  border: none;
+  background: transparent;
+  color: var(--text-tertiary);
+  cursor: pointer;
+  border-radius: var(--radius-sm);
+  transition: color $transition-fast;
+
+  &:hover:not(:disabled) {
+    color: var(--text-primary);
+  }
+
+  &:disabled {
+    opacity: 0.5;
+    cursor: not-allowed;
+  }
+}
+
 .entriesList {
   display: flex;
   flex-direction: column;