feat: blocked task state for agent questions via session resume

When an agent needs user input it writes a question to
$CLAUDOMATOR_QUESTION_FILE and exits. The runner detects the file and
returns BlockedError; the pool transitions the task to BLOCKED and
stores the question JSON on the task record.

The user answers via POST /api/tasks/{id}/answer. The server looks up
the claude session_id from the most recent execution and submits a
resume execution (claude --resume <session-id> "<answer>"), freeing the
executor slot entirely while waiting.

Changes:
- task: add StateBlocked, transitions RUNNING→BLOCKED, BLOCKED→QUEUED
- storage: add session_id to executions, question_json to tasks;
  add GetLatestExecution and UpdateTaskQuestion methods
- executor: BlockedError type; ClaudeRunner pre-assigns --session-id,
  sets CLAUDOMATOR_QUESTION_FILE env var, detects question file on exit;
  buildArgs handles --resume mode; Pool.SubmitResume for resume path
- api: handleAnswerQuestion rewritten to create resume execution
- preamble: add question protocol instructions for agents
- web: BLOCKED state badge (indigo), question text + option buttons or
  free-text input with Submit on the task card footer

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

1 files changed, 18 insertions, 1 deletions

diff --git a/internal/executor/preamble.go b/internal/executor/preamble.go
index cd1a2cc..8a2cce3 100644
--- a/internal/executor/preamble.go
+++ b/internal/executor/preamble.go
@@ -1,6 +1,23 @@
 package executor
 
-const planningPreamble = `## Planning Step (do this first)
+const planningPreamble = `## Runtime Environment
+
+You are running as a background agent inside Claudomator. You cannot interact
+with the user directly. However, if you need a decision or clarification:
+
+**To ask the user a question and pause:**
+1. Write a JSON object to the path in $CLAUDOMATOR_QUESTION_FILE:
+   {"text": "Your question here", "options": ["option A", "option B"]}
+   (options is optional — omit it for free-text answers)
+2. Exit immediately. Do not wait. The task will be resumed with the user's answer
+   as the next message in this conversation.
+
+Only ask a question when truly blocked. Prefer making a reasonable decision
+and noting it in your output.
+
+---
+
+## Planning Step (do this first)
 
 Before doing any implementation work: