feat(settings): tabbed MCP install instructions with Claude Code flow

Replace the hand-edit-JSON instructions in Settings → API Keys with a
tabbed UI (Claude Code / Claude Desktop / Other). The Claude Code tab
leads with the `claude mcp add` command, pre-filled with FABLE_URL and
the most recently generated API key, plus copy-to-clipboard buttons on
every snippet. Recommend `uv tool install` or `pipx install` over bare
`pip install` so fable-mcp reliably lands on PATH under PEP 668.

Also fix incorrect priority values in fable-mcp tool docstrings — the
enum is `none|low|medium|high`, not `low|normal|high`.

DRY pass: extract shared `copyToClipboard()` helper used by both
`copyApiKey` and the new snippet buttons; reuse existing
`btn btn-secondary btn-sm` for the copy buttons instead of a bespoke
class.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fable-mcp/fable_mcp/server.py

@@ -27,7 +27,7 @@ The hierarchy is: Project → Milestone → Task/Note.
 
 - **Tasks** belong to a project and optionally a milestone. They support sub-tasks via `parent_id`.
   - Status values: `todo`, `in_progress`, `done`, `cancelled`
-  - Priority values: `low`, `normal`, `high`
+  - Priority values: `none` (default), `low`, `medium`, `high`
 
 - **Notes** are free-form markdown documents. They can belong to a project or be standalone
   (orphan notes). Orphan notes are included in the default RAG scope for chat conversations.
@@ -241,7 +241,7 @@ async def fable_create_task(
         title: Task title (required).
         body: Markdown description / notes for the task.
         status: Initial status — one of: todo (default), in_progress, done, cancelled.
-        priority: One of: low, normal, high. Omit for no priority.
+        priority: One of: low, medium, high. Omit for no priority (defaults to "none").
         project_id: Associate with a project (0 = no project).
         milestone_id: Place within a project milestone (0 = no milestone).
         parent_id: Make this a sub-task of another task (0 = top-level).
@@ -280,7 +280,7 @@ async def fable_update_task(
         title: New title, or omit to leave unchanged.
         body: New markdown body, or omit to leave unchanged.
         status: New status — one of: todo, in_progress, done, cancelled.
-        priority: New priority — one of: low, normal, high.
+        priority: New priority — one of: none, low, medium, high.
         project_id: New project (0 = remove from project). Omit to leave unchanged.
         milestone_id: New milestone (0 = remove from milestone). Omit to leave unchanged.
     """