fix(docs): repair the contributing guide content defects

Mechanical repairs to the guide, each anchored on a known-broken form:

- substituted {{FORGE}}

No prose is rewritten; only the broken forms are corrected.

Author: hyperpolymath

.github/CONTRIBUTING.md

@@ -1,5 +1,5 @@
 # Clone the repository
-git clone https://{{FORGE}}/hyperpolymath/patch-bridge.git
+git clone https://github.com/hyperpolymath/patch-bridge.git
 cd patch-bridge
 
 # Using Nix (recommended for reproducibility)
@@ -91,10 +91,10 @@ Use the [feature request template](.github/ISSUE_TEMPLATE/feature_request.md) an
 
 Look for issues labelled:
 
-- [`good first issue`](https://{{FORGE}}/hyperpolymath/patch-bridge/labels/good%20first%20issue) — Simple Perimeter 3 tasks
-- [`help wanted`](https://{{FORGE}}/hyperpolymath/patch-bridge/labels/help%20wanted) — Community help needed
-- [`documentation`](https://{{FORGE}}/hyperpolymath/patch-bridge/labels/documentation) — Docs improvements
-- [`perimeter-3`](https://{{FORGE}}/hyperpolymath/patch-bridge/labels/perimeter-3) — Community sandbox scope
+- [`good first issue`](https://github.com/hyperpolymath/patch-bridge/labels/good%20first%20issue) — Simple Perimeter 3 tasks
+- [`help wanted`](https://github.com/hyperpolymath/patch-bridge/labels/help%20wanted) — Community help needed
+- [`documentation`](https://github.com/hyperpolymath/patch-bridge/labels/documentation) — Docs improvements
+- [`perimeter-3`](https://github.com/hyperpolymath/patch-bridge/labels/perimeter-3) — Community sandbox scope
 
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