docs: move ADRs to project root, remove boilerplate README

Move `doc/adr/` to `adr/` for discoverability. Remove the generic
ADR README — `ls adr/` serves the same purpose.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

doc/adr/README.md

@@ -1,38 +0,0 @@
-# Architecture Decision Records
-
-This directory contains Architecture Decision Records (ADRs) for the cheat project.
-
-## What is an ADR?
-
-An Architecture Decision Record captures an important architectural decision made along with its context and consequences. ADRs help us:
-
-- Document why decisions were made
-- Understand the context and trade-offs
-- Review decisions when requirements change
-- Onboard new contributors
-
-## ADR Format
-
-Each ADR follows this template:
-
-1. **Title**: ADR-NNN: Brief description
-2. **Date**: When the decision was made
-3. **Status**: Proposed, Accepted, Deprecated, Superseded
-4. **Context**: What prompted this decision?
-5. **Decision**: What did we decide to do?
-6. **Consequences**: What are the positive, negative, and neutral outcomes?
-
-## Index of ADRs
-
-| ADR | Title | Status | Date |
-|-----|-------|--------|------|
-| [001](001-path-traversal-protection.md) | Path Traversal Protection for Cheatsheet Names | Accepted | 2025-01-21 |
-| [002](002-environment-variable-parsing.md) | No Defensive Checks for Environment Variable Parsing | Accepted | 2025-01-21 |
-| [003](003-search-parallelization.md) | No Parallelization for Search Operations | Accepted | 2025-01-22 |
-
-## Creating a New ADR
-
-1. Copy the template from an existing ADR
-2. Use the next sequential number
-3. Fill in all sections
-4. Include the ADR alongside the commit implementing the decision