fix(config): load global config when HOME is missing on Windows

[JohnsonRan]

Problem

On Windows, Node/Pi can run without HOME (or with HOME empty). Global config writers already use process.env.HOME || os.homedir(), but resolveConfig and migrateUserMemoryConfigFiles only inspect env.HOME. A saved ~/.pi/agent/hindsight.json or hindsight.jsonc configuration is therefore ignored, and its legacy User Bank keys are not migrated.

Expected behavior

Resolve and migrate global hindsight.json/hindsight.jsonc using an explicit nonempty HOME, otherwise node:os homedir(). Preserve project and environment override precedence and migration backups.

Scope and acceptance

• Align the two config-loading/migration paths with the existing writer fallback.
• Add isolated regression coverage for missing/empty HOME, explicit HOME, project/env overrides and migration backups.
• Run targeted tests, npm run check, npm run check:coverage and npm run typecheck:tsc. Document live-smoke availability and request cross-platform CI for this Windows-sensitive fix.

Existing local fix is being prepared as a focused PR; no package or lockfile changes.

[JohnsonRan]

Opened #632 with the focused two-file HOME fallback fix (commit f7f84d2). Regression proof: the two missing/empty-HOME tests fail before the fix; all 28 config tests pass after it. npm run check, npm run check:coverage, npm run typecheck:tsc, and normal Git hooks passed locally (710 passed, 1 existing skip; Windows canonical TEMP/TMP and bounded workers). Live smoke passed temporary bank creation, Retain and Recall, but Reflect returned HTTP 524; temporary-bank cleanup succeeded. Full live proof remains incomplete. Please apply ci:full for cross-platform CI and complete live-smoke verification before merging. Leaving this issue open until the PR is merged.