fix: resolve 5 remaining pre-publish blockers (14, 15, 17, 21, 25c)

- completion-promise-detector: restrict to assistant text parts only,
  remove tool_result from completion detection (blocker 14)
- ralph-loop tests: flip tool_result completion expectations to negative
  coverage, add false-positive rejection tests (blocker 15)
- skill tools: merge nativeSkills into initial cachedDescription
  synchronously before any execute() call (blocker 17)
- skill tools test: add assertion for initial description including
  native skills before execute() (blocker 25c)
- docs: sync all 4 fallback-chain docs with model-requirements.ts
  runtime source of truth (blocker 21)

Verified: bun test (4599 pass / 0 fail), tsc --noEmit clean

src/hooks/ralph-loop/completion-promise-detector.test.ts

@@ -110,7 +110,7 @@ describe("detectCompletionInSessionMessages", () => {
   })
 
   describe("#given promise appears in tool_result part (not text part)", () => {
-    test("#when Oracle returns VERIFIED via task() tool_result #then should detect completion", async () => {
+    test("#when Oracle returns VERIFIED via task() tool_result #then should NOT detect completion", async () => {
       const messages: SessionMessage[] = [
         {
           info: { role: "assistant" },
@@ -137,10 +137,10 @@ describe("detectCompletionInSessionMessages", () => {
         sinceMessageIndex: 0,
       })
 
-      expect(detected).toBe(true)
+      expect(detected).toBe(false)
     })
 
-    test("#when DONE appears only in tool_result part #then should detect completion", async () => {
+    test("#when DONE appears only in tool_result part #then should NOT detect completion", async () => {
       const messages: SessionMessage[] = [
         {
           info: { role: "assistant" },
@@ -159,7 +159,7 @@ describe("detectCompletionInSessionMessages", () => {
         directory: "/tmp",
       })
 
-      expect(detected).toBe(true)
+      expect(detected).toBe(false)
     })
 
     test("#when promise appears in tool_use part (not tool_result) #then should NOT detect completion", async () => {