feat: add profiles — run multiple isolated Hermes instances (#3681)

Each profile is a fully independent HERMES_HOME with its own config,
API keys, memory, sessions, skills, gateway, cron, and state.db.

Core module: hermes_cli/profiles.py (~900 lines)
  - Profile CRUD: create, delete, list, show, rename
  - Three clone levels: blank, --clone (config), --clone-all (everything)
  - Export/import: tar.gz archive for backup and migration
  - Wrapper alias scripts (~/.local/bin/<name>)
  - Collision detection for alias names
  - Sticky default via ~/.hermes/active_profile
  - Skill seeding via subprocess (handles module-level caching)
  - Auto-stop gateway on delete with disable-before-stop for services
  - Tab completion generation for bash and zsh

CLI integration (hermes_cli/main.py):
  - _apply_profile_override(): pre-import -p/--profile flag + sticky default
  - Full 'hermes profile' subcommand: list, use, create, delete, show,
    alias, rename, export, import
  - 'hermes completion bash/zsh' command
  - Multi-profile skill sync in hermes update

Display (cli.py, banner.py, gateway/run.py):
  - CLI prompt: 'coder ❯' when using a non-default profile
  - Banner shows profile name
  - Gateway startup log includes profile name

Gateway safety:
  - Token locks: Discord, Slack, WhatsApp, Signal (extends Telegram pattern)
  - Port conflict detection: API server, webhook adapter

Diagnostics (hermes_cli/doctor.py):
  - Profile health section: lists profiles, checks config, .env, aliases
  - Orphan alias detection: warns when wrapper points to deleted profile

Tests (tests/hermes_cli/test_profiles.py):
  - 71 automated tests covering: validation, CRUD, clone levels, rename,
    export/import, active profile, isolation, alias collision, completion
  - Full suite: 6760 passed, 0 new failures

Documentation:
  - website/docs/user-guide/profiles.md: full user guide (12 sections)
  - website/docs/reference/profile-commands.md: command reference (12 commands)
  - website/docs/reference/faq.md: 6 profile FAQ entries
  - website/sidebars.ts: navigation updated

website/docs/developer-guide/contributing.md

@@ -90,6 +90,7 @@ pytest tests/ -v
 - **Comments**: Only when explaining non-obvious intent, trade-offs, or API quirks
 - **Error handling**: Catch specific exceptions. Use `logger.warning()`/`logger.error()` with `exc_info=True` for unexpected errors
 - **Cross-platform**: Never assume Unix (see below)
+- **Profile-safe paths**: Never hardcode `~/.hermes` — use `get_hermes_home()` from `hermes_constants` for code paths and `display_hermes_home()` for user-facing messages. See [AGENTS.md](https://github.com/NousResearch/hermes-agent/blob/main/AGENTS.md#profiles-multi-instance-support) for full rules.
 
 ## Cross-Platform Compatibility