refactor(#1281): T2 — migrate 12 single-leaf callers off the core spine (batch 1) (#1282)

Per the T1 design rubber-duck, batch by FILE so each tranche drops
convergence-lint allowlist entries. Migrate 12 files' core imports to the
leaf modules directly (behaviour-identical — leaves are the objects core
re-exports by reference):
- io (output/error/ERROR_REASON): agent-command-router, capability-state,
  capability-writer, frontmatter, gsd2-import, learnings, loop-resolver,
  task-command-router
- roadmap-command-router -> config-loader; workstream-inventory -> core-utils
- milestone, verify -> their full leaf sets (both were multi-leaf, not
  single-leaf as first scoped; migrated completely)

All 12 files now import zero core symbols and are removed from the
allowlist (30 -> 18). core.cts re-exports untouched (still serve the
remaining 18 files); teardown is T-final. Stale core.cjs docstrings in the
migrated files corrected to reference io.cjs. No behaviour change.

Closes #1281

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

src/milestone.cts

@@ -8,8 +8,6 @@
 
 import fs from 'node:fs';
 import path from 'node:path';
-// eslint-disable-next-line @typescript-eslint/no-require-imports -- core.cjs is an export= CommonJS module
-import core = require('./core.cjs');
 // eslint-disable-next-line @typescript-eslint/no-require-imports -- planning-workspace.cjs is an export= CommonJS module
 import planningWorkspace = require('./planning-workspace.cjs');
 // eslint-disable-next-line @typescript-eslint/no-require-imports -- frontmatter.cjs is an export= CommonJS module
@@ -18,16 +16,18 @@ import frontmatterMod = require('./frontmatter.cjs');
 import stateMod = require('./state.cjs');
 import { platformWriteSync, platformEnsureDir } from './shell-command-projection.cjs';
 import { formatGsdSlash, resolveRuntime } from './runtime-slash.cjs';
-
-const {
-  escapeRegex,
-  getMilestonePhaseFilter,
-  extractOneLinerFromBody,
-  normalizePhaseName,
-  phaseTokenMatches,
-  output,
-  error,
-} = core;
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+import ioMod = require('./io.cjs');
+const { output, error } = ioMod;
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+import phaseIdMod = require('./phase-id.cjs');
+const { escapeRegex, normalizePhaseName, phaseTokenMatches } = phaseIdMod;
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+import roadmapParserMod = require('./roadmap-parser.cjs');
+const { getMilestonePhaseFilter, extractCurrentMilestone } = roadmapParserMod;
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+import coreUtilsMod = require('./core-utils.cjs');
+const { extractOneLinerFromBody } = coreUtilsMod;
 const { planningPaths } = planningWorkspace;
 const { extractFrontmatter } = frontmatterMod;
 const { writeStateMd, stateReplaceFieldWithFallback } = stateMod;
@@ -167,7 +167,6 @@ function cmdMilestoneComplete(cwd: string, version: string, options: MilestoneCo
       }
 
       if (stateVersion && stateVersion === version) {
-        const { extractCurrentMilestone } = core;
         const roadmapContent = fs.readFileSync(roadmapPath, 'utf-8');
         const scopedContent = extractCurrentMilestone(roadmapContent, cwd);
         const phasePattern = /#{2,4}\s*Phase\s+(\d+[A-Z]?(?:\.\d+)*)\s*:\s*([^\n]+)/gi;