Add detailed file index and enhance skill documentation for autopilot, decompose, deploy, plan, and research skills. Introduce tests-only mode in decompose skill, clarify required files for deploy and plan skills, and improve prerequisite checks across skills for better user guidance and workflow efficiency.

.cursor/skills/plan/steps/00_prerequisites.md

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+## Prerequisite Checks (BLOCKING)
+
+Run sequentially before any planning step:
+
+### Prereq 1: Data Gate
+
+1. `_docs/00_problem/acceptance_criteria.md` exists and is non-empty — **STOP if missing**
+2. `_docs/00_problem/restrictions.md` exists and is non-empty — **STOP if missing**
+3. `_docs/00_problem/input_data/` exists and contains at least one data file — **STOP if missing**
+4. `_docs/00_problem/problem.md` exists and is non-empty — **STOP if missing**
+
+All four are mandatory. If any is missing or empty, STOP and ask the user to provide them. If the user cannot provide the required data, planning cannot proceed — just stop.
+
+### Prereq 2: Finalize Solution Draft
+
+Only runs after the Data Gate passes:
+
+1. Scan `_docs/01_solution/` for files matching `solution_draft*.md`
+2. Identify the highest-numbered draft (e.g. `solution_draft06.md`)
+3. **Rename** it to `_docs/01_solution/solution.md`
+4. If `solution.md` already exists, ask the user whether to overwrite or keep existing
+5. Verify `solution.md` is non-empty — **STOP if missing or empty**
+
+### Prereq 3: Workspace Setup
+
+1. Create DOCUMENT_DIR if it does not exist
+2. If DOCUMENT_DIR already contains artifacts, ask user: **resume from last checkpoint or start fresh?**