fix(docs): list the contributing guide where it actually lives

The repository-structure block listed `CONTRIBUTING.md` at the repository
root, but the guide lives at `.github/CONTRIBUTING.md` - the entry pointed
at a location it had already moved away from. The entry is moved under the
tree's existing `.github/` branch, at the block's own comment column; the
layout of the rest of the tree is untouched.

Author: hyperpolymath

.github/CONTRIBUTING.md

@@ -16,27 +16,26 @@ just test    # Run test suite
 ```
 
 ### Repository Structure
-
-```text
+```
 patch-bridge/
-├── src/ # Source code (Perimeter 1-2)
-├── lib/ # Library code (Perimeter 1-2)
-├── extensions/ # Extensions (Perimeter 2)
-├── plugins/ # Plugins (Perimeter 2)
-├── tools/ # Tooling (Perimeter 2)
-├── docs/ # Documentation (Perimeter 3)
-│   ├── architecture/ # ADRs, specs (Perimeter 2)
-│   └── proposals/ # RFCs (Perimeter 3)
-├── examples/ # Examples (Perimeter 3)
-├── spec/ # Spec tests (Perimeter 3)
-├── tests/ # Test suite (Perimeter 2-3)
-├── .machine_readable/ # ALL machine-readable content (Perimeter 1)
-│   ├── *.a2ml # State files (STATE, META, ECOSYSTEM, etc.)
-│   ├── bot_directives/ # Bot configs
-│   └── contractiles/ # Policy contracts (k9, dust, lust, must, trust)
-├── .well-known/ # Protocol files (Perimeter 1-3)
-├── .github/ # GitHub config (Perimeter 1)
-│   ├── CONTRIBUTING.md # This file
+├── src/                 # Source code (Perimeter 1-2)
+├── lib/                 # Library code (Perimeter 1-2)
+├── extensions/          # Extensions (Perimeter 2)
+├── plugins/             # Plugins (Perimeter 2)
+├── tools/               # Tooling (Perimeter 2)
+├── docs/                # Documentation (Perimeter 3)
+│   ├── architecture/    # ADRs, specs (Perimeter 2)
+│   └── proposals/       # RFCs (Perimeter 3)
+├── examples/            # Examples (Perimeter 3)
+├── spec/                # Spec tests (Perimeter 3)
+├── tests/               # Test suite (Perimeter 2-3)
+├── .machine_readable/   # ALL machine-readable content (Perimeter 1)
+│   ├── *.a2ml           # State files (STATE, META, ECOSYSTEM, etc.)
+│   ├── bot_directives/  # Bot configs
+│   └── contractiles/    # Policy contracts (k9, dust, lust, must, trust)
+├── .well-known/         # Protocol files (Perimeter 1-3)
+├── .github/             # GitHub config (Perimeter 1)
+│   ├── CONTRIBUTING.md  # This file
 │   ├── ISSUE_TEMPLATE/
 │   └── workflows/
 ├── CHANGELOG.md
@@ -46,9 +45,9 @@ patch-bridge/
 ├── MAINTAINERS.md
 ├── README.adoc
 ├── SECURITY.md
-├── flake.nix # Nix flake — fallback (Perimeter 1)
-├── guix.scm # Guix package — primary (Perimeter 1)
-└── Justfile # Task runner (Perimeter 1) ```
+├── flake.nix            # Nix flake — fallback (Perimeter 1)
+├── guix.scm             # Guix package — primary (Perimeter 1)
+└── Justfile             # Task runner (Perimeter 1)
 ```
 
 ---