feat(#1173): wire the 8 agent converters into the descriptor-driven install path

The descriptor-driven install path (resolveRuntimeArtifactLayout) installed no
agents for copilot/antigravity/cursor/windsurf/augment/trae/codebuddy/cline —
their per-runtime agent conversion ran only via the legacy bin/install.js loop.
This wires each runtime's agent converter into the descriptor so the new path
applies per-runtime conversion (follow-up to #1099; ADR-1235 cutover).

- capabilities/<rt>/capability.json: declare an `agents` kind with the runtime's
  converter (global+local; cline global-only). Regenerated capability-registry.cjs.
- convertedAgentsKind threads install scope -> isGlobal so the scope-aware
  copilot/antigravity converters choose global vs workspace-relative paths; the
  six single-arg converters ignore the extra arg. stageAgentsForRuntimeWithConverter
  passes isGlobal to the converter.
- Tests: feat-1173 gains a real-registry block asserting each runtime's descriptor
  applies the correct converter (== conv(src, isGlobal), != raw copy) with scope
  threading (fails-first on pristine next). The ADR-857 equivalence golden +
  per-runtime kind-count assertions now include the agents kind, each annotated as
  an intentional #1173 change.

Scope: this wires the per-runtime CONVERTER. The remaining byte-parity behaviors of
the legacy loop (copilot `.agent.md` rename, cross-cutting path/attribution rewrites,
config-reading) stay with the legacy loop -- which runs after installRuntimeArtifacts
and is authoritative for the real install -- and are tracked by ADR-1235's later
cutover steps. No user-facing change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/install-profiles.cts

@@ -548,12 +548,16 @@ function stageSkillsForRuntimeAsSkills(
  *
  * @param srcAgentsDir    source agents directory (e.g. agents/)
  * @param resolvedProfile profile filter from resolveProfile()
- * @param converter       (content: string) → string  pure per-file converter
+ * @param converter       (content: string, isGlobal?: boolean) → string per-file
+ *                        converter; scope-aware converters (copilot/antigravity)
+ *                        read isGlobal, single-arg converters ignore it (#1173)
+ * @param isGlobal        install scope passed through to the converter
  */
 function stageAgentsForRuntimeWithConverter(
   srcAgentsDir: string,
   resolvedProfile: ResolvedProfile,
-  converter: (content: string) => string,
+  converter: (content: string, isGlobal?: boolean) => string,
+  isGlobal = false,
 ): string {
   if (!fs.existsSync(srcAgentsDir)) return srcAgentsDir;
 
@@ -571,7 +575,7 @@ function stageAgentsForRuntimeWithConverter(
         }
       }
       const content = fs.readFileSync(path.join(srcAgentsDir, entry.name), 'utf8');
-      const converted = converter(content);
+      const converted = converter(content, isGlobal);
       fs.writeFileSync(path.join(stageDir, entry.name), converted, 'utf8');
     }
   } catch (err) {