feat: add source hyperlinks + remove thin from-source.md

Every source reference now links to elixir-lang/elixir at commit f4e1b34.
122 hyperlinks across 11 topic files. Added PATTERN_COMPLETE sentinels.
Removed from-source.md (326 lines, shallow) — covered by existing files.

smells/anti-patterns.md

@@ -1035,3 +1035,5 @@ end
 ```
 
 **Why it's OK here:** The dispatch is by configured module (strategy pattern), not by data type. You want compile-time verification that the storage module implements all required operations. A protocol wouldn't help because the data going in is always the same type — it's the *implementation* that varies.
+
+<!-- PATTERN_COMPLETE -->