refactor: extract shared settings stylesheet (pg.css) and clean up inline styles

- Create cortex/static/pg.css with shared variables, nav, containers, form
  elements, button classes, text utilities, and feedback messages
- All four settings pages (settings, notifications, tools, help) now link to
  pg.css and have page-specific-only <style> blocks
- Style block line counts reduced: settings 244→70, notifications 189→42,
  tools 126→88, help 122→75
- Inline style= attributes reduced: settings 45→4, notifications 7→3,
  tools 12→4, help 0
- Introduced shared CSS classes: .btn-submit, .btn-save, .btn-cancel,
  .btn-secondary, .action-link, .hint, .section-note, .page-title,
  .page-subtitle, .page-wrap, .usage-table, .tool-cat-row
- Fix tools_settings.py: replace server-generated inline styles on category
  header rows with .tool-cat-row CSS class
- Fix settings.py: add btn-save/btn-cancel/persona-rename-cancel classes to
  server-rendered persona rename form buttons

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/routers/settings.py

@@ -127,8 +127,8 @@ def _settings_page(username: str, personas: list[str], back_persona: str = "", s
             <input type="hidden" name="old_name" value="{p}">
             <input type="text" name="new_name" value="{p}"
                    pattern="[a-z_][a-z0-9_\\-]{{0,31}}" required>
-            <button type="submit">Save</button>
-            <button type="button" class="persona-rename-cancel">Cancel</button>
+            <button type="submit" class="btn-save">Save</button>
+            <button type="button" class="btn-cancel persona-rename-cancel">Cancel</button>
           </form>
         </li>''' for p in personas
     )

cortex/routers/tools_settings.py

@@ -53,13 +53,7 @@ def _build_tool_table(policy: dict) -> str:
     for category, tools in TOOL_CATEGORIES.items():
         # Category header spanning all columns
         escaped_cat = _html.escape(category)
-        rows.append(
-            f'<tr><td colspan="4" style="padding:0.75rem 0.9rem 0.3rem;'
-            f'font-size:0.72rem;font-weight:700;letter-spacing:0.07em;'
-            f'text-transform:uppercase;color:var(--pg-dimmer);'
-            f'border-bottom:1px solid var(--pg-border);">'
-            f'{escaped_cat}</td></tr>'
-        )
+        rows.append(f'<tr class="tool-cat-row"><td colspan="4">{escaped_cat}</td></tr>')
         for tool in tools:
             risk      = TOOL_RISK.get(tool, "medium")
             risk_cls  = f"risk-{risk}"