feat(skills): skill system + load_skill tool via per-turn tools filter

Skills are markdown in .skills/ dirs (~/.skills + <cwd>/.skills, cwd shadows home;
name = filename). Format: line1 summary, line2 ---, body line3+; load strips the
first two lines; malformed = no summary but still loadable.

Mechanism (first use of the context-assembly filter chain, §3.2):
- kernel: expose HostAPI.applyFilters (delegates to bus.applyFilters)
- session-orchestrator: define/export toolsFilter + ToolAssembly; apply once per turn
  before runTurn (cache-stable across steps), threading cwd + conversationId
- skills (new ext): pure parse/merge/render + load_skill tool (live read, path-contained)
  + a toolsFilter filter rewriting load_skill's description + name enum per cwd
- host-bin: register skills in CORE_EXTENSIONS
- transport-http: fix HostAPI test stub for the new applyFilters method (fan-out)

734 vitest + 109 bun = 843 tests; tsc -b EXIT 0; biome clean; clean live boot.

1 files changed, 11 insertions, 0 deletions

diff --git a/bun.lock b/bun.lock
index 3cd4cc8..e1c62d6 100644
--- a/bun.lock
+++ b/bun.lock
@@ -51,6 +51,7 @@
         "@dispatch/kernel": "workspace:*",
         "@dispatch/provider-openai-compat": "workspace:*",
         "@dispatch/session-orchestrator": "workspace:*",
+        "@dispatch/skills": "workspace:*",
         "@dispatch/storage-sqlite": "workspace:*",
         "@dispatch/surface-loaded-extensions": "workspace:*",
         "@dispatch/surface-registry": "workspace:*",
@@ -102,6 +103,14 @@
         "@dispatch/kernel": "workspace:*",
       },
     },
+    "packages/skills": {
+      "name": "@dispatch/skills",
+      "version": "0.0.0",
+      "dependencies": {
+        "@dispatch/kernel": "workspace:*",
+        "@dispatch/session-orchestrator": "workspace:*",
+      },
+    },
     "packages/storage-sqlite": {
       "name": "@dispatch/storage-sqlite",
       "version": "0.0.0",
@@ -252,6 +261,8 @@
 
     "@dispatch/session-orchestrator": ["@dispatch/session-orchestrator@workspace:packages/session-orchestrator"],
 
+    "@dispatch/skills": ["@dispatch/skills@workspace:packages/skills"],
+
     "@dispatch/storage-sqlite": ["@dispatch/storage-sqlite@workspace:packages/storage-sqlite"],
 
     "@dispatch/surface-loaded-extensions": ["@dispatch/surface-loaded-extensions@workspace:packages/surface-loaded-extensions"],