refactor(#1756): derive getDirName from a documented runtime.localConfigDir descriptor axis (#1757)

ADR-1239 Phase B (parent #1679). getDirName was a hand-maintained 15-branch
if-chain mapping each runtime to its local content-rewrite dot-dir. Relocate
those values into a documented runtime.localConfigDir descriptor field; derive
getDirName from registry.runtimes[id].runtime.localConfigDir (fallback .claude).

- 16 capability.json gain runtime.localConfigDir (byte-identical values)
- capability-validator.cjs requires it (non-empty dot-dir); registry regenerated
- docs/reference/capability-manifest.md documents the field + the three
  divergent values (copilot=.github, antigravity=.agents, kimi=.kimi-code)
- drift-guard test: golden value map + key-set equality both ways

Byte-identical install output for all 16 runtimes (golden-parity harness #1730).

Closes #1756

Co-authored-by: review-bot <review-bot@gsd>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

capabilities/antigravity/capability.json

@@ -24,6 +24,7 @@
       ],
       "probeExists": "gsd-core/VERSION"
     },
+    "localConfigDir": ".agents",
     "configFormat": "settings-json",
     "artifactLayout": {
       "global": [

capabilities/augment/capability.json

@@ -17,6 +17,7 @@
         "AUGMENT_CONFIG_DIR"
       ]
     },
+    "localConfigDir": ".augment",
     "configFormat": "settings-json",
     "artifactLayout": {
       "global": [

capabilities/claude/capability.json

@@ -17,6 +17,7 @@
         "CLAUDE_CONFIG_DIR"
       ]
     },
+    "localConfigDir": ".claude",
     "configFormat": "settings-json",
     "artifactLayout": {
       "global": [

capabilities/cline/capability.json

@@ -17,6 +17,7 @@
         "CLINE_CONFIG_DIR"
       ]
     },
+    "localConfigDir": ".cline",
     "configFormat": "markdown-dir",
     "artifactLayout": {
       "global": [

capabilities/codebuddy/capability.json

@@ -17,6 +17,7 @@
         "CODEBUDDY_CONFIG_DIR"
       ]
     },
+    "localConfigDir": ".codebuddy",
     "configFormat": "settings-json",
     "artifactLayout": {
       "global": [

capabilities/codex/capability.json

@@ -17,6 +17,7 @@
         "CODEX_HOME"
       ]
     },
+    "localConfigDir": ".codex",
     "configFormat": "toml",
     "artifactLayout": {
       "global": [

capabilities/copilot/capability.json

@@ -18,6 +18,7 @@
         "COPILOT_HOME"
       ]
     },
+    "localConfigDir": ".github",
     "configFormat": "markdown",
     "artifactLayout": {
       "global": [

capabilities/cursor/capability.json

@@ -17,6 +17,7 @@
         "CURSOR_CONFIG_DIR"
       ]
     },
+    "localConfigDir": ".cursor",
     "configFormat": "none",
     "artifactLayout": {
       "global": [

capabilities/gemini/capability.json

@@ -17,6 +17,7 @@
         "GEMINI_CONFIG_DIR"
       ]
     },
+    "localConfigDir": ".gemini",
     "configFormat": "settings-json",
     "artifactLayout": {
       "global": [

capabilities/hermes/capability.json

@@ -17,6 +17,7 @@
         "HERMES_HOME"
       ]
     },
+    "localConfigDir": ".hermes",
     "configFormat": "settings-json",
     "artifactLayout": {
       "global": [

capabilities/kilo/capability.json

@@ -24,6 +24,7 @@
         "env": []
       }
     },
+    "localConfigDir": ".kilo",
     "configFormat": "settings-json",
     "artifactLayout": {
       "global": [

capabilities/kimi/capability.json

@@ -22,6 +22,7 @@
       ],
       "probeExists": "skills"
     },
+    "localConfigDir": ".kimi-code",
     "configFormat": "none",
     "artifactLayout": {
       "global": [

capabilities/opencode/capability.json

@@ -19,6 +19,7 @@
         "XDG_CONFIG_HOME"
       ]
     },
+    "localConfigDir": ".opencode",
     "configFormat": "settings-json",
     "artifactLayout": {
       "global": [

capabilities/qwen/capability.json

@@ -17,6 +17,7 @@
         "QWEN_CONFIG_DIR"
       ]
     },
+    "localConfigDir": ".qwen",
     "configFormat": "settings-json",
     "artifactLayout": {
       "global": [

capabilities/trae/capability.json

@@ -17,6 +17,7 @@
         "TRAE_CONFIG_DIR"
       ]
     },
+    "localConfigDir": ".trae",
     "configFormat": "none",
     "artifactLayout": {
       "global": [

capabilities/windsurf/capability.json

@@ -18,6 +18,7 @@
         "WINDSURF_CONFIG_DIR"
       ]
     },
+    "localConfigDir": ".windsurf",
     "configFormat": "none",
     "artifactLayout": {
       "global": [],