docs: Add specs and tasks for previously scoped work in todo.md

.config/dot/.claude/tasks/0003-kde-schema-backed-diff.md

@@ -0,0 +1,27 @@
+---
+spec: dot-kde
+blocked-by: 0001-kde-schema-backed-save
+---
+
+## What to build
+
+Implement `dot kde diff`'s broad, read-only scan for schema-backed
+settings: walk every `(rcfile, group, key)` reachable through the
+mapping table built in the prior task, compare each live value
+(`kreadconfig6`) against its schema-declared default, and report every
+mismatch. Each reported mismatch is tagged as declared (its identifier is
+present in the manifest — an intentional, already-tracked deviation) or
+undeclared (never explicitly declared). `diff` never writes anything.
+Add `dot kde diff help`, following the project's
+check-for-`help`-before-`argparse` convention.
+
+Add a README row for `dot kde diff`.
+
+## Acceptance criteria
+
+- [ ] `dot kde diff` reports every schema-backed setting whose live value differs from its schema-declared default
+- [ ] Each reported mismatch is tagged declared or undeclared based on manifest presence
+- [ ] `dot kde diff` makes no writes under any circumstances
+- [ ] `dot kde diff help` prints usage without scanning
+- [ ] Tests run against a scratch `$HOME` and fixture `.kcfg` schema directory, covering: a declared mismatch, an undeclared mismatch, and a setting matching its default (not reported)
+- [ ] README has a row for `dot kde diff`