refactor(#1675): dedup augment converter family — single-source from conversion module (#1685)

bin/install.js held byte-identical duplicate definitions of the augment
converter family (convertSlashCommandsToAugmentSkillMentions,
convertClaudeToAugmentMarkdown, getAugmentSkillAdapterHeader,
convertClaudeCommandToAugmentSkill, convertClaudeAgentToAugmentAgent) that
already exist canonically in src/runtime-artifact-conversion.cts (generated
to gsd-core/bin/lib/runtime-artifact-conversion.cjs). Deferred Phase 1->2
cleanup tracked in #1675 (epic #1507 / ADR-1508).

Deleted the five local copies; install.js now binds the three PUBLIC
converters from runtimeArtifactConversion (same pattern as getDirName /
processAttribution in #1510). The two private helpers live only in the
conversion module now. module.exports preserved (re-exported).

Behavior-preserving: four converters byte-identical; the fifth
(convertClaudeAgentToAugmentAgent) differed only by an inert let->const
(variable never reassigned). Extends the DEFECT.GENERATIVE-FIX
reference-identity parity guard in enh-1511 to assert single-sourcing.

Closes #1675

tests/enh-1511-rewrite-engine-relocation.test.cjs

@@ -378,4 +378,31 @@ describe('single-owner reference-identity guard (ADR-1508 / #1511 Phase 2)', ()
       'install.js must bind _applyRuntimeRewrites from conversion (not a local shim)',
     );
   });
+
+  // #1675 (ADR-1508): the augment converter family is single-sourced in the
+  // conversion module. install.js must re-bind (not re-define) these so there
+  // is exactly one body — the generative-drift hazard the dedup removes.
+  test('install.convertClaudeToAugmentMarkdown === conversion.convertClaudeToAugmentMarkdown (single converter)', () => {
+    assert.strictEqual(
+      install.convertClaudeToAugmentMarkdown,
+      conversionCjs.convertClaudeToAugmentMarkdown,
+      'install.js must bind convertClaudeToAugmentMarkdown from conversion (not a duplicate body)',
+    );
+  });
+
+  test('install.convertClaudeCommandToAugmentSkill === conversion.convertClaudeCommandToAugmentSkill (single converter)', () => {
+    assert.strictEqual(
+      install.convertClaudeCommandToAugmentSkill,
+      conversionCjs.convertClaudeCommandToAugmentSkill,
+      'install.js must bind convertClaudeCommandToAugmentSkill from conversion (not a duplicate body)',
+    );
+  });
+
+  test('install.convertClaudeAgentToAugmentAgent === conversion.convertClaudeAgentToAugmentAgent (single converter)', () => {
+    assert.strictEqual(
+      install.convertClaudeAgentToAugmentAgent,
+      conversionCjs.convertClaudeAgentToAugmentAgent,
+      'install.js must bind convertClaudeAgentToAugmentAgent from conversion (not a duplicate body)',
+    );
+  });
 });