feat: implement new claude skills and workflow

.claude/skills/doc-sync/README.md

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+# Doc Sync
+
+The CLAUDE.md/README.md hierarchy is central to context hygiene. CLAUDE.md files
+are pure indexes -- tabular navigation with "What" and "When to read" columns
+that help LLMs (and humans) find relevant files without loading everything.
+README.md files capture invisible knowledge: architecture decisions, design
+tradeoffs, and invariants that are not apparent from reading code.
+
+The doc-sync skill audits and synchronizes this hierarchy across a repository.
+
+## How It Works
+
+The skill operates in five phases:
+
+1. **Discovery** -- Maps all directories, identifies missing or outdated
+   CLAUDE.md files
+2. **Audit** -- Checks for drift (files added/removed but not indexed),
+   misplaced content (architecture docs in CLAUDE.md instead of README.md)
+3. **Migration** -- Moves architectural content from CLAUDE.md to README.md
+4. **Update** -- Creates/updates indexes with proper tabular format
+5. **Verification** -- Confirms complete coverage and correct structure
+
+## When to Use
+
+Use this skill for:
+
+- **Bootstrapping** -- Adopting this workflow on an existing repository
+- **After bulk changes** -- Major refactors, directory restructuring
+- **Periodic audits** -- Checking for documentation drift
+- **Onboarding** -- Before starting work on an unfamiliar codebase
+
+If you use the planning workflow consistently, the technical writer agent
+maintains documentation as part of execution. As such, doc-sync is primarily for
+bootstrapping or recovery -- not routine use.
+
+## Example Usage
+
+```
+Use your doc-sync skill to synchronize documentation across this repository
+```
+
+For targeted updates:
+
+```
+Use your doc-sync skill to update documentation in src/validators/
+```