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.

website/docs/reference/cli-commands.md

@@ -62,6 +62,7 @@ hermes [global-options] <command> [subcommand/options]
 | `hermes config` | Show, edit, migrate, and query configuration files. |
 | `hermes pairing` | Approve or revoke messaging pairing codes. |
 | `hermes skills` | Browse, install, publish, audit, and configure skills. |
+| `hermes bundles` | Group several skills under a single `/<name>` slash command. See [Skill Bundles](../user-guide/features/skills.md#skill-bundles). |
 | `hermes curator` | Background skill maintenance — status, run, pause, pin. See [Curator](../user-guide/features/curator.md). |
 | `hermes memory` | Configure external memory provider. Plugin-specific subcommands (e.g. `hermes honcho`) register automatically when their provider is active. |
 | `hermes acp` | Run Hermes as an ACP server for editor integration. |
@@ -825,6 +826,40 @@ Notes:
 - `--source well-known` lets you point Hermes at a site exposing `/.well-known/skills/index.json`.
 - Passing an `http(s)://…/*.md` URL installs a single-file SKILL.md directly. When frontmatter has no `name:` and the URL slug isn't a valid identifier, an interactive terminal prompts for a name; non-interactive surfaces (`/skills install` inside the TUI, gateway platforms) require `--name <x>` instead.
 
+## `hermes bundles`
+
+```bash
+hermes bundles <subcommand>
+```
+
+Skill bundles group several skills under one `/<bundle-name>` slash command. Invoking the bundle loads every referenced skill into a single combined user message. Storage: `~/.hermes/skill-bundles/<slug>.yaml`. See [Skill Bundles](../user-guide/features/skills.md#skill-bundles) for the YAML schema and behavior.
+
+Subcommands:
+
+| Subcommand | Description |
+|------------|-------------|
+| `list` | List installed bundles (default when no subcommand given) |
+| `show <name>` | Show one bundle's name, description, skills, and file path |
+| `create <name>` | Create a new bundle. Pass `--skill <id>` (repeat) or omit for interactive entry. `--description`, `--instruction`, `--force` available. |
+| `delete <name>` | Remove a bundle file |
+| `reload` | Re-scan `~/.hermes/skill-bundles/` and report added/removed bundles |
+
+Examples:
+
+```bash
+hermes bundles create backend-dev \
+  --skill github-code-review \
+  --skill test-driven-development \
+  --skill github-pr-workflow \
+  -d "Backend feature work"
+
+hermes bundles list
+hermes bundles show backend-dev
+hermes bundles delete backend-dev
+```
+
+In a chat session, `/bundles` lists installed bundles and `/<bundle-name>` loads one.
+
 ## `hermes curator`
 
 ```bash