feat(skills): add skill bundles — alias /<name> loads multiple skills (#28373)

Skill bundles are tiny YAML files in ~/.hermes/skill-bundles/ that
group several skills under one slash command. Invoking /<bundle-name>
from any surface (CLI, TUI, dashboard, any gateway platform) loads
every referenced skill into a single combined user message.

Use cases:
- /backend-dev → loads github-code-review + test-driven-development
  + github-pr-workflow as one bundle.
- /research → loads several research skills together.
- Team task profiles shared via dotfiles.

Behavior:
- Bundles take precedence over individual skills when slugs collide.
- Missing skills are skipped with a note, not fatal.
- No system-prompt mutation — bundles generate a fresh user message
  at invocation time, the same way /<skill> does. Prompt cache stays
  intact.
- Works in CLI dispatch, gateway dispatch, autocomplete (CLI + TUI),
  /help display.

Schema (~/.hermes/skill-bundles/<slug>.yaml):
    name: backend-dev
    description: Backend feature work.
    skills:
      - github-code-review
      - test-driven-development
    instruction: |
      Optional extra guidance prepended to the loaded skills.

New module: agent/skill_bundles.py — load, scan, resolve, build
invocation message, save, delete. yaml.safe_load only; broken
bundles log a warning and are skipped, never raise.

New CLI subcommand: hermes bundles {list,show,create,delete,reload}.
Implementation in hermes_cli/bundles.py; wired in hermes_cli/main.py.
'bundles' added to _BUILTIN_SUBCOMMANDS so plugin discovery skips it.

New in-session slash command: /bundles lists installed bundles in
both CLI and gateway. /<bundle-name> dispatch added to CLI (cli.py)
and gateway (gateway/run.py) before the existing /<skill-name> path.

Autocomplete: SlashCommandCompleter gained an optional
skill_bundles_provider parameter that defaults to None — the prompt
shows '▣ <description> (N skills)' for bundles vs '⚡' for skills.

Tests:
- tests/agent/test_skill_bundles.py — 33 tests covering slugify,
  scan/cache freshness, resolve (including underscore→hyphen
  Telegram alias), build_bundle_invocation_message (loading, missing
  skills, user/bundle instruction injection, dedup), save/delete,
  reload diff, list sort.
- tests/hermes_cli/test_bundles.py — 8 tests for the CLI
  subcommand (create/list/show/delete/reload, --force, missing
  bundle errors).
- tests/gateway/test_bundles_command.py — 4 tests for the gateway
  handler and bundle resolution priority.

Live E2E: verified subprocess invocations of hermes bundles
{list,create,show,reload,delete} round-trip correctly against an
isolated HERMES_HOME.

Docs:
- website/docs/user-guide/features/skills.md — new 'Skill Bundles'
  section with quick example, YAML schema, management commands,
  behavior notes.
- website/docs/reference/cli-commands.md — 'hermes bundles' added to
  the top-level command table and given its own subcommand section.

hermes_cli/main.py

@@ -9904,7 +9904,7 @@ def _build_provider_choices() -> list[str]:
 # to parse.
 _BUILTIN_SUBCOMMANDS = frozenset(
     {
-        "acp", "auth", "backup", "checkpoints", "claw", "completion",
+        "acp", "auth", "backup", "bundles", "checkpoints", "claw", "completion",
         "computer-use",
         "config", "cron", "curator", "dashboard", "debug", "doctor",
         "dump", "fallback", "gateway", "hooks", "import", "insights",
@@ -11338,6 +11338,22 @@ Examples:
 
     skills_parser.set_defaults(func=cmd_skills)
 
+    # =========================================================================
+    # bundles command — skill bundles (alias /<name> for multiple skills)
+    # =========================================================================
+    bundles_parser = subparsers.add_parser(
+        "bundles",
+        help="Create, list, and manage skill bundles (aliases for multiple skills)",
+        description=(
+            "Skill bundles let you load several skills under one slash "
+            "command. `/<bundle>` from the CLI or gateway loads every "
+            "referenced skill at once."
+        ),
+    )
+    from hermes_cli.bundles import register_cli as _bundles_register, bundles_command
+    _bundles_register(bundles_parser)
+    bundles_parser.set_defaults(func=bundles_command)
+
     # =========================================================================
     # plugins command
     # =========================================================================