merge: origin/main v1.0.0.0 into garrytan/fix-checkpoints

Main shipped the v1 prompts rewrite (simpler writing style + real LOC
receipts + /plan-tune observational substrate). Resolved conflicts:

- VERSION / package.json: bumped 0.18.5.0 → 1.0.1.0 (main is 1.0.0.0,
  this branch lands next).
- CHANGELOG: moved the /context-save + /context-restore entry to the
  top as v1.0.1.0, above main's v1.0.0.0. Also removed the em-dash
  variants in the new entry (ship voice rule).
- TODOS: kept both sections — Context skills (lane feature TODO) first,
  main's PACING_UPDATES_V0 + Plan Tune v2 deferrals below.
- Migration: renamed gstack-upgrade/migrations/v0.18.5.0.sh →
  v1.0.1.0.sh (matches new version). Test path updated.

preamble.ts auto-merged cleanly: main's question-tuning, explain_level,
and writing-style sections composed with my context-save/context-restore
routing rule.

All SKILL.md files regenerated via `bun run gen:skill-docs --host all`
per CLAUDE.md's "never resolve generated files by accepting either
side" rule. Golden fixtures (claude/codex/factory ship) also regenerated.

bun test: 0 failures.

test/migration-checkpoint-ownership.test.ts

@@ -5,7 +5,7 @@ import * as path from 'path';
 import * as os from 'os';
 
 const ROOT = path.resolve(import.meta.dir, '..');
-const MIGRATION = path.join(ROOT, 'gstack-upgrade', 'migrations', 'v0.18.5.0.sh');
+const MIGRATION = path.join(ROOT, 'gstack-upgrade', 'migrations', 'v1.0.1.0.sh');
 
 function runMigration(tmpHome: string): { exitCode: number; stdout: string; stderr: string } {
   const result = spawnSync('bash', [MIGRATION], {
@@ -28,7 +28,7 @@ function setupFakeGstackRoot(tmpHome: string): string {
   return gstackDir;
 }
 
-describe('migration v0.18.5.0 — checkpoint ownership guard', () => {
+describe('migration v1.0.1.0 — checkpoint ownership guard', () => {
   let tmpHome: string;
 
   beforeEach(() => {