feat(dev-workflow): Add intelligent backend selection based on task complexity (#61)

合并智能 backend 选择功能。包含：multiSelect backend 选择、type 字段任务分类(default|ui|quick-fix)、智能路由策略

dev-workflow/README.md

@@ -9,42 +9,56 @@ A freshly designed lightweight development workflow with no legacy baggage, focu
 ```
 /dev trigger
   ↓
+AskUserQuestion (backend selection)
+  ↓
 AskUserQuestion (requirements clarification)
   ↓
-codeagent analysis (plan mode + UI auto-detection)
+codeagent analysis (plan mode + task typing + UI auto-detection)
   ↓
 dev-plan-generator (create dev doc)
   ↓
-codeagent concurrent development (2–5 tasks, backend split)
+codeagent concurrent development (2–5 tasks, backend routing)
   ↓
 codeagent testing & verification (≥90% coverage)
   ↓
 Done (generate summary)
 ```
 
-## The 6 Steps
+## Step 0 + The 6 Steps
+
+### 0. Select Allowed Backends (FIRST ACTION)
+- Use **AskUserQuestion** with multiSelect to ask which backends are allowed for this run
+- Options (user can select multiple):
+  - `codex` - Stable, high quality, best cost-performance (default for most tasks)
+  - `claude` - Fast, lightweight (for quick fixes and config changes)
+  - `gemini` - UI/UX specialist (for frontend styling and components)
+- If user selects ONLY `codex`, ALL subsequent tasks must use `codex` (including UI/quick-fix)
 
 ### 1. Clarify Requirements
 - Use **AskUserQuestion** to ask the user directly
 - No scoring system, no complex logic
 - 2–3 rounds of Q&A until the requirement is clear
 
-### 2. codeagent Analysis & UI Detection
+### 2. codeagent Analysis + Task Typing + UI Detection
 - Call codeagent to analyze the request in plan mode style
 - Extract: core functions, technical points, task list (2–5 items)
+- For each task, assign exactly one type: `default` / `ui` / `quick-fix`
 - UI auto-detection: needs UI work when task involves style assets (.css, .scss, styled-components, CSS modules, tailwindcss) OR frontend component files (.tsx, .jsx, .vue); output yes/no plus evidence
 
 ### 3. Generate Dev Doc
 - Call the **dev-plan-generator** agent
 - Produce a single `dev-plan.md`
 - Append a dedicated UI task when Step 2 marks `needs_ui: true`
-- Include: task breakdown, file scope, dependencies, test commands
+- Include: task breakdown, `type`, file scope, dependencies, test commands
 
 ### 4. Concurrent Development
 - Work from the task list in dev-plan.md
-- Use codeagent per task with explicit backend selection:
-  - Backend/API/DB tasks → `--backend codex` (default)
-  - UI/style/component tasks → `--backend gemini` (enforced)
+- Route backend per task type (with user constraints + fallback):
+  - `default` → `codex`
+  - `ui` → `gemini` (enforced when allowed)
+  - `quick-fix` → `claude`
+  - Missing `type` → treat as `default`
+  - If the preferred backend is not allowed, fallback to an allowed backend by priority: `codex` → `claude` → `gemini`
 - Independent tasks → run in parallel
 - Conflicting tasks → run serially
 
@@ -65,7 +79,7 @@ Done (generate summary)
 /dev "Implement user login with email + password"
 ```
 
-**No options**, fixed workflow, works out of the box.
+No CLI flags required; workflow starts with an interactive backend selection.
 
 ## Output Structure
 
@@ -80,14 +94,14 @@ Only one file—minimal and clear.
 
 ### Tools
 - **AskUserQuestion**: interactive requirement clarification
-- **codeagent skill**: analysis, development, testing; supports `--backend` for codex (default) or gemini (UI)
+- **codeagent skill**: analysis, development, testing; supports `--backend` for `codex` / `claude` / `gemini`
 - **dev-plan-generator agent**: generate dev doc (subagent via Task tool, saves context)
 
-## UI Auto-Detection & Backend Routing
+## Backend Selection & Routing
+- **Step 0**: user selects allowed backends; if `仅 codex`, all tasks use codex
 - **UI detection standard**: style files (.css, .scss, styled-components, CSS modules, tailwindcss) OR frontend component code (.tsx, .jsx, .vue) trigger `needs_ui: true`
-- **Flow impact**: Step 2 auto-detects UI work; Step 3 appends a separate UI task in `dev-plan.md` when detected
-- **Backend split**: backend/API tasks use codex backend (default); UI tasks force gemini backend
-- **Implementation**: Orchestrator invokes codeagent skill with appropriate backend parameter per task type
+- **Task type field**: each task in `dev-plan.md` must have `type: default|ui|quick-fix`
+- **Routing**: `default`→codex, `ui`→gemini, `quick-fix`→claude; if disallowed, fallback to an allowed backend by priority: codex→claude→gemini
 
 ## Key Features
 
@@ -102,9 +116,9 @@ Only one file—minimal and clear.
 - Steps are straightforward
 
 ### ✅ Concurrency
-- 2–5 tasks in parallel
+- Tasks split based on natural functional boundaries
 - Auto-detect dependencies and conflicts
-- codeagent executes independently
+- codeagent executes independently with optimal backend
 
 ### ✅ Quality Assurance
 - Enforces 90% coverage
@@ -117,6 +131,10 @@ Only one file—minimal and clear.
 # Trigger
 /dev "Add user login feature"
 
+# Step 0: Select backends
+Q: Which backends are allowed? (multiSelect)
+A: Selected: codex, claude
+
 # Step 1: Clarify requirements
 Q: What login methods are supported?
 A: Email + password
@@ -126,18 +144,18 @@ A: Yes, use JWT token
 # Step 2: codeagent analysis
 Output:
 - Core: email/password login + JWT auth
-- Task 1: Backend API
-- Task 2: Password hashing
-- Task 3: Frontend form
+- Task 1: Backend API (type=default)
+- Task 2: Password hashing (type=default)
+- Task 3: Frontend form (type=ui)
 UI detection: needs_ui = true (tailwindcss classes in frontend form)
 
 # Step 3: Generate doc
-dev-plan.md generated with backend + UI tasks ✓
+dev-plan.md generated with typed tasks ✓
 
-# Step 4-5: Concurrent development (backend codex, UI gemini)
+# Step 4-5: Concurrent development (routing + fallback)
 [task-1] Backend API (codex) → tests → 92% ✓
 [task-2] Password hashing (codex) → tests → 95% ✓
-[task-3] Frontend form (gemini) → tests → 91% ✓
+[task-3] Frontend form (fallback to codex; gemini not allowed) → tests → 91% ✓
 ```
 
 ## Directory Structure