feat(skills): blank-slate skills — install --no-skills + opt-out/opt-in (#36228)

* feat(install): --no-skills flag for blank-slate default profile

Add an install-time --no-skills flag so the default ~/.hermes profile can
be created with zero bundled skills, matching what
`hermes profile create --no-skills` already does for named profiles.

The flag writes $HERMES_HOME/.no-bundled-skills and skips the install-time
seed. sync_skills() now honors that marker with an early return
(skipped_opt_out=True), so neither the installer, a later `hermes update`,
nor a direct sync re-injects bundled skills into a profile that opted out.

Previously the marker was only checked by seed_profile_skills() (named
profiles); the default profile had no opt-out and `hermes update` would
re-seed it every time.

Tests: TestNoBundledSkillsOptOut covers marker-present (no-op) and
marker-absent (normal seed) paths.

* feat(skills): hermes skills opt-out / opt-in for existing profiles

Adds an interactive counterpart to the install-time --no-skills flag so
an already-installed profile (default or named) can toggle the
.no-bundled-skills marker without reinstalling.

- `hermes skills opt-out` writes the marker (stop future seeding). Safe
  by default: nothing on disk is touched.
- `hermes skills opt-out --remove` ALSO deletes already-present bundled
  skills, but ONLY ones that are manifest-tracked AND byte-identical to
  their origin hash. User-edited bundled skills, hub-installed skills, and
  hand-written skills are never removed. Previews + confirms before
  deleting (--yes to skip).
- `hermes skills opt-in [--sync]` removes the marker and optionally
  re-seeds immediately.

Core logic lives in tools/skills_sync.py (set_bundled_skills_opt_out,
is_bundled_skills_opt_out, remove_pristine_bundled_skills) reusing the
existing manifest origin-hash machinery for the safety check.

Tests: TestOptOutToggleAndRemove covers marker toggle idempotency and
proves user-modified + non-bundled skills survive --remove.

* docs: blank-slate skills — install --no-skills + opt-out/opt-in

- features/skills.md: new 'Starting with a blank slate' section covering
  the install flag, profile-create flag, and runtime opt-out/opt-in, with
  a safe-by-default note.
- reference/cli-commands.md: document the new skills opt-out / opt-in
  subcommands + examples.
- reference/profile-commands.md: fix the marker filename (was .no-skills,
  actually .no-bundled-skills) and cross-link the runtime commands.

Validated with a full docusaurus build (exit 0); the three edited pages
compile clean with no new warnings.

website/docs/user-guide/features/skills.md

@@ -17,6 +17,36 @@ See also:
 - [Bundled Skills Catalog](/reference/skills-catalog)
 - [Official Optional Skills Catalog](/reference/optional-skills-catalog)
 
+## Starting with a blank slate
+
+By default every profile is seeded with the bundled skill catalog, and each `hermes update` adds any newly bundled skills. If you want a profile with **no bundled skills** — and that stays empty across updates — you have two paths:
+
+**At install time** (applies to the default `~/.hermes` profile):
+
+```bash
+curl -fsSL https://hermes-agent.nousresearch.com/install.sh | bash -s -- --no-skills
+```
+
+**At profile-create time** (named profiles):
+
+```bash
+hermes profile create research --no-skills
+```
+
+**On an already-installed profile** (default or named), toggle it at runtime:
+
+```bash
+hermes skills opt-out            # stop future seeding — nothing on disk is touched
+hermes skills opt-out --remove   # also delete UNMODIFIED bundled skills (confirms first)
+hermes skills opt-in --sync      # undo: remove the marker and re-seed now
+```
+
+All three paths write a `.no-bundled-skills` marker into the profile directory. While the marker is present, the installer, `hermes update`, and any skill sync all skip bundled-skill seeding for that profile. Delete the marker (or run `hermes skills opt-in`) to re-enable.
+
+:::note Safe by default
+`hermes skills opt-out` only stops *future* seeding — it never deletes anything already on disk. The optional `--remove` flag deletes bundled skills **only** when they are unmodified (byte-identical to the version Hermes installed). Skills you have edited, skills installed from the hub, and skills you wrote yourself are always kept.
+:::
+
 ## Using Skills
 
 Every installed skill is automatically available as a slash command: