feat(config): add OPENCLAUDE_CONFIG_DIR env var as preferred alias for CLAUDE_CONFIG_DIR (#454)

The legacy CLAUDE_CONFIG_DIR name was the only way to point openclaude
at a non-default config home, which leaked Anthropic branding for a
fork that has otherwise rebranded to OpenClaude. Add OPENCLAUDE_CONFIG_DIR
as the preferred name. CLAUDE_CONFIG_DIR continues to work for
backward compatibility; when both are set with different values,
OPENCLAUDE_CONFIG_DIR wins and a one-time warning is logged.

- src/utils/envUtils.ts: introduce resolveConfigDirEnv() that picks
  OPENCLAUDE_CONFIG_DIR over CLAUDE_CONFIG_DIR and emits a conflict
  warning. Memoize cache key now tracks both env vars so changing
  either invalidates the cached result.
- src/utils/env.ts: getGlobalClaudeFile() previously read
  CLAUDE_CONFIG_DIR directly, missing the new alias. Route through
  resolveConfigDirEnv() so the global config file path follows the
  same precedence.
- src/utils/secureStorage/macOsKeychainHelpers.ts: the "is default
  dir" check used by keychain service-name scoping now considers
  both env vars.
- src/utils/swarm/spawnUtils.ts: forward OPENCLAUDE_CONFIG_DIR to
  teammate processes alongside the legacy var.
- src/utils/openclaudePaths.test.ts: +6 unit tests covering the new
  alias, fallthrough, conflict warning, and resolveConfigDirEnv()
  in isolation.
- .env.example: document both env vars and the precedence rule.

Verified locally on Linux: with only OPENCLAUDE_CONFIG_DIR set, with
only CLAUDE_CONFIG_DIR set (legacy still works), with both set
matching (silent), with both set conflicting (warn once + OPENCLAUDE
wins), with neither set (default ~/.openclaude). Memo cache
invalidates across 4 sequential env transitions. Built dist/cli.mjs
honors the new var and emits the conflict warning to the user.

.env.example

@@ -421,3 +421,16 @@ ANTHROPIC_API_KEY=sk-ant-your-key-here
 # WEB_CUSTOM_ALLOW_HTTP=false                — set "true" to allow http:// URLs
 # WEB_CUSTOM_ALLOW_PRIVATE=false             — set "true" to target localhost/private IPs
 #                                               (needed for self-hosted SearXNG)
+
+# ── Config directory override ───────────────────────────────────────
+#
+# By default openclaude stores per-user state under ~/.openclaude
+# (and falls back to ~/.claude for installs that pre-date the rename).
+# Set this to point openclaude at a different directory — useful for
+# isolating profiles or sharing config across machines.
+#
+# OPENCLAUDE_CONFIG_DIR=/path/to/dir         — preferred name
+# CLAUDE_CONFIG_DIR=/path/to/dir             — legacy alias (still works)
+#
+# When both are set with different values, OPENCLAUDE_CONFIG_DIR wins
+# and a warning is logged once per process.