refactor: orchestrator pre-selects features for all agents

Replace agent-initiated feature selection with orchestrator pre-selection
for both coding and testing agents. This ensures Mission Control displays
correct feature numbers for testing agents (previously showed "Feature #0").

Key changes:

MCP Server (mcp_server/feature_mcp.py):
- Add feature_get_by_id tool for agents to fetch assigned feature details
- Remove obsolete tools: feature_get_next, feature_claim_next,
  feature_claim_for_testing, feature_get_for_regression
- Remove helper functions and unused imports (text, OperationalError, func)

Orchestrator (parallel_orchestrator.py):
- Change running_testing_agents from list to dict[int, Popen]
- Add claim_feature_for_testing() with random selection
- Add release_testing_claim() method
- Pass --testing-feature-id to spawned testing agents
- Use unified [Feature #X] output format for both agent types

Agent Entry Points:
- autonomous_agent_demo.py: Add --testing-feature-id CLI argument
- agent.py: Pass testing_feature_id to get_testing_prompt()

Prompt Templates:
- coding_prompt.template.md: Update to use feature_get_by_id
- testing_prompt.template.md: Update workflow for pre-assigned features
- prompts.py: Update pre-claimed headers for both agent types

WebSocket (server/websocket.py):
- Simplify tracking with unified [Feature #X] pattern
- Remove testing-specific parsing code

Assistant (server/services/assistant_chat_session.py):
- Update help text with current available tools

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

server/services/assistant_chat_session.py

@@ -47,8 +47,9 @@ API_ENV_VARS = [
 # Read-only feature MCP tools
 READONLY_FEATURE_MCP_TOOLS = [
     "mcp__features__feature_get_stats",
-    "mcp__features__feature_get_next",
-    "mcp__features__feature_get_for_regression",
+    "mcp__features__feature_get_by_id",
+    "mcp__features__feature_get_ready",
+    "mcp__features__feature_get_blocked",
 ]
 
 # Feature management tools (create/skip but not mark_passing)
@@ -124,8 +125,9 @@ If the user asks you to modify code, explain that you're a project assistant and
 
 **Feature Management:**
 - **feature_get_stats**: Get feature completion progress
-- **feature_get_next**: See the next pending feature
-- **feature_get_for_regression**: See passing features for testing
+- **feature_get_by_id**: Get details for a specific feature
+- **feature_get_ready**: See features ready for implementation
+- **feature_get_blocked**: See features blocked by dependencies
 - **feature_create**: Create a single feature in the backlog
 - **feature_create_bulk**: Create multiple features at once
 - **feature_skip**: Move a feature to the end of the queue