docs(agents): add few-shot calibration examples for plan-checker and verifier (#1792)

* docs(agents): add few-shot calibration examples for plan-checker and verifier

Closes #1723

* test(agents): add structural tests for few-shot calibration examples

Validates reference file existence, frontmatter metadata, example counts,
WHY annotations on every example, agent @reference lines, and content
structure (input/output pairs, calibration gap patterns table).

agents/gsd-plan-checker.md

@@ -83,6 +83,9 @@ Same methodology (goal-backward), different timing, different subject matter.
 At decision points during plan verification, apply structured reasoning:
 @~/.claude/get-shit-done/references/thinking-models-planning.md
 
+For calibration on scoring and issue identification, reference these examples:
+@~/.claude/get-shit-done/references/few-shot-examples/plan-checker.md
+
 ## Dimension 1: Requirement Coverage
 
 **Question:** Does every phase requirement have task(s) addressing it?

agents/gsd-verifier.md

@@ -60,6 +60,9 @@ Then verify each level against the actual codebase.
 At verification decision points, apply structured reasoning:
 @~/.claude/get-shit-done/references/thinking-models-verification.md
 
+At verification decision points, reference calibration examples:
+@~/.claude/get-shit-done/references/few-shot-examples/verifier.md
+
 ## Step 0: Check for Previous Verification
 
 ```bash