chore: add shared skills catalog (19 skills), installers, manifest, validator

skills/systematic-debugging/SKILL.md

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+---
+name: systematic-debugging
+description: Use when debugging complex bugs, unexpected test failures, race conditions, or production anomalies. Enforces a rigorous scientific debugging method over trial-and-error edits.
+---
+
+# Systematic Debugging — The Scientific Method for Bug Fixing
+
+## Core Discipline
+Never guess, shotgun edit, or apply speculative fixes without proving the root cause. Follow the 5-phase scientific debugging loop.
+
+## Phase 1: Reproduce & Isolate
+1. **Deterministic Reproduction:** Create a minimal, self-contained test case or command that reliably reproduces the failure.
+2. **Eliminate Variables:** Strip away unrelated components, mocks, or background noise.
+3. **Capture Ground Truth:** Inspect actual inputs, outputs, error codes, and stack traces — do not rely on memory or assumptions.
+
+## Phase 2: Formulate Hypotheses
+1. Brainstorm candidate root causes based on observed behavior.
+2. Rank hypotheses by likelihood.
+3. For each hypothesis, define an empirical test: *"If hypothesis X is true, observing Y will yield Z."*
+
+## Phase 3: Test Hypotheses (Binary Search & Instrumentation)
+1. Add targeted logs, breakpoints, or assertion guards at key boundary points.
+2. Use bisection (git bisect or code division) to narrow down when/where state deviates from expected invariants.
+3. Invalidate or confirm hypotheses one by one.
+
+## Phase 4: Root Cause Fix
+1. Fix the underlying design flaw, invariant violation, or race condition — not just the symptom.
+2. Verify that the fix does not break related code or introduce regressions.
+3. Clean up all temporary debug logging and instrumentation.
+
+## Phase 5: Regression Prevention
+1. Commit the automated reproduction test (unit/integration test) alongside the fix.
+2. Add explicit invariants or typing to prevent this class of bug at compile or boot time.