refactor: decouple rulespec from plan_write, read from analysis/rulespec.yaml

- Remove rulespec parameter from plan_write tool definition and execution
- Remove rulespec compilation from plan_approve (no longer pre-compiles)
- Remove write_rulespec, get_rulespec_path, format_rulespec_yaml/markdown
  from invariants.rs; read_rulespec() now takes &Path working dir
- Remove save/load_compiled_rulespec, get_compiled_rulespec_path from datalog.rs
- Update shadow_datalog_verify() to compile on-the-fly from
  analysis/rulespec.yaml, writing rulespec.compiled.dl and
  datalog_evaluation.txt to session dir
- Remove rulespec display from plan_read output
- Remove Invariants/Rulespec section from native.md system prompt
- Remove rulespec from prompts.rs plan_write format and examples
- Update existing tests to remove rulespec from plan_write calls
- Add 3 integration tests for on-the-fly rulespec verification

crates/g3-core/src/tool_definitions.rs

@@ -192,17 +192,13 @@ fn create_core_tools() -> Vec<Tool> {
 
     tools.push(Tool {
         name: "plan_write".to_string(),
-        description: "Create or update the Plan for this session. For NEW plans, you MUST provide both 'plan' and 'rulespec' arguments. The rulespec defines invariants (constraints that must/must not hold) extracted from the task and memory. For plan UPDATES, rulespec is optional.".to_string(),
+        description: "Create or update the Plan for this session. Provide the plan as YAML with plan_id, revision, and items array.".to_string(),
         input_schema: json!({
             "type": "object",
             "properties": {
                 "plan": {
                     "type": "string",
                     "description": "The plan as YAML. Must include plan_id and items array."
-                },
-                "rulespec": {
-                    "type": "string",
-                    "description": "The rulespec as YAML with claims and predicates. REQUIRED for new plans, optional for updates. Defines invariants from task_prompt and memory."
                 }
             },
             "required": ["plan"]