feat(discord): register skills under /skill command group with category subcommands (#9909)

Instead of consuming one top-level slash command slot per skill (hitting the
100-command limit with ~26 built-ins + 74 skills), skills are now organized
under a single /skill group command with category-based subcommand groups:

  /skill creative ascii-art [args]
  /skill media gif-search [args]
  /skill mlops axolotl [args]

Discord supports 25 subcommand groups × 25 subcommands = 625 max skills,
well beyond the previous 74-slot ceiling.

Categories are derived from the skill directory structure:
- skills/creative/ascii-art/ → category 'creative'
- skills/mlops/training/axolotl/ → category 'mlops' (top-level parent)
- skills/dogfood/ → uncategorized (direct subcommand)

Changes:
- hermes_cli/commands.py: add discord_skill_commands_by_category() with
  category grouping, hub/disabled filtering, Discord limit enforcement
- gateway/platforms/discord.py: replace top-level skill registration with
  _register_skill_group() using app_commands.Group hierarchy
- tests: 7 new tests covering group creation, category grouping,
  uncategorized skills, hub exclusion, deep nesting, empty skills,
  and handler dispatch

Inspired by Discord community suggestion from bottium.

gateway/platforms/discord.py

@@ -1736,46 +1736,90 @@ class DiscordAdapter(BasePlatformAdapter):
         async def slash_btw(interaction: discord.Interaction, question: str):
             await self._run_simple_slash(interaction, f"/btw {question}")
 
-        # Register installed skills as native slash commands (parity with
-        # Telegram, which uses telegram_menu_commands() in commands.py).
-        # Discord allows up to 100 application commands globally.
-        _DISCORD_CMD_LIMIT = 100
+        # Register skills under a single /skill command group with category
+        # subcommand groups.  This uses 1 top-level slot instead of N,
+        # supporting up to 25 categories × 25 skills = 625 skills.
+        self._register_skill_group(tree)
+
+    def _register_skill_group(self, tree) -> None:
+        """Register a ``/skill`` command group with category subcommand groups.
+
+        Skills are organized by their directory category under ``SKILLS_DIR``.
+        Each category becomes a subcommand group; root-level skills become
+        direct subcommands.  Discord supports 25 subcommand groups × 25
+        subcommands each = 625 skills — well beyond the old 100-command cap.
+        """
         try:
-            from hermes_cli.commands import discord_skill_commands
+            from hermes_cli.commands import discord_skill_commands_by_category
 
-            existing_names = {cmd.name for cmd in tree.get_commands()}
-            remaining_slots = max(0, _DISCORD_CMD_LIMIT - len(existing_names))
+            existing_names = set()
+            try:
+                existing_names = {cmd.name for cmd in tree.get_commands()}
+            except Exception:
+                pass
 
-            skill_entries, skipped = discord_skill_commands(
-                max_slots=remaining_slots,
+            categories, uncategorized, hidden = discord_skill_commands_by_category(
                 reserved_names=existing_names,
             )
 
-            for discord_name, description, cmd_key in skill_entries:
-                # Closure factory to capture cmd_key per iteration
-                def _make_skill_handler(_key: str):
-                    async def _skill_slash(interaction: discord.Interaction, args: str = ""):
-                        await self._run_simple_slash(interaction, f"{_key} {args}".strip())
-                    return _skill_slash
+            if not categories and not uncategorized:
+                return
 
-                handler = _make_skill_handler(cmd_key)
-                handler.__name__ = f"skill_{discord_name.replace('-', '_')}"
+            skill_group = discord.app_commands.Group(
+                name="skill",
+                description="Run a Hermes skill",
+            )
 
+            # ── Helper: build a callback for a skill command key ──
+            def _make_handler(_key: str):
+                @discord.app_commands.describe(args="Optional arguments for the skill")
+                async def _handler(interaction: discord.Interaction, args: str = ""):
+                    await self._run_simple_slash(interaction, f"{_key} {args}".strip())
+                _handler.__name__ = f"skill_{_key.lstrip('/').replace('-', '_')}"
+                return _handler
+
+            # ── Uncategorized (root-level) skills → direct subcommands ──
+            for discord_name, description, cmd_key in uncategorized:
                 cmd = discord.app_commands.Command(
                     name=discord_name,
-                    description=description,
-                    callback=handler,
+                    description=description or f"Run the {discord_name} skill",
+                    callback=_make_handler(cmd_key),
                 )
-                discord.app_commands.describe(args="Optional arguments for the skill")(cmd)
-                tree.add_command(cmd)
+                skill_group.add_command(cmd)
 
-            if skipped:
+            # ── Category subcommand groups ──
+            for cat_name in sorted(categories):
+                cat_desc = f"{cat_name.replace('-', ' ').title()} skills"
+                if len(cat_desc) > 100:
+                    cat_desc = cat_desc[:97] + "..."
+                cat_group = discord.app_commands.Group(
+                    name=cat_name,
+                    description=cat_desc,
+                    parent=skill_group,
+                )
+                for discord_name, description, cmd_key in categories[cat_name]:
+                    cmd = discord.app_commands.Command(
+                        name=discord_name,
+                        description=description or f"Run the {discord_name} skill",
+                        callback=_make_handler(cmd_key),
+                    )
+                    cat_group.add_command(cmd)
+
+            tree.add_command(skill_group)
+
+            total = sum(len(v) for v in categories.values()) + len(uncategorized)
+            logger.info(
+                "[%s] Registered /skill group: %d skill(s) across %d categories"
+                " + %d uncategorized",
+                self.name, total, len(categories), len(uncategorized),
+            )
+            if hidden:
                 logger.warning(
-                    "[%s] Discord slash command limit reached (%d): %d skill(s) not registered",
-                    self.name, _DISCORD_CMD_LIMIT, skipped,
+                    "[%s] %d skill(s) not registered (Discord subcommand limits)",
+                    self.name, hidden,
                 )
         except Exception as exc:
-            logger.warning("[%s] Failed to register skill slash commands: %s", self.name, exc)
+            logger.warning("[%s] Failed to register /skill group: %s", self.name, exc)
 
     def _build_slash_event(self, interaction: discord.Interaction, text: str) -> MessageEvent:
         """Build a MessageEvent from a Discord slash command interaction."""