fix: nomarchy-manual opens local README, not an Omarchy URL

The script hardcoded `xdg-open https://learn.omacom.io/2/the-nomarchy-manual`
— an upstream Omarchy page. Users hitting "Help → Manual" in nomarchy-menu
were sent to an unrelated site, and there's no nomarchy.org canonical
docs URL to point at instead.

Now opens `$HOME/.local/share/nomarchy/README.md`, which lives on every
installed system (per SKILL.md's "Out of Scope" note about
`~/.local/share/nomarchy/`) and links every doc in `docs/`. Falls back
to a notify-send "run nomarchy-update?" message if the source tree
isn't synced.

Pillar 6 entry in docs/ROADMAP.md updated to (Shipped).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/SCRIPTS.md

@@ -169,7 +169,7 @@ Phase B (per-batch PRs) refines those into `port-from-omarchy`,
 | `nomarchy-tui-remove` | `features/scripts/utils` | core/home/config/nomarchy-skill/SKILL.md | `kept` |  |
 | `nomarchy-tui-remove-all` | `features/scripts/utils` | core/home/config/nomarchy-skill/SKILL.md | `kept` |  |
 | `nomarchy-tz-select` | `core/system/scripts` | features/desktop/waybar/config/config.jsonc,features/scripts/utils/nomarchy-menu, +2 more | `kept` |  |
-| `nomarchy-update` | `core/system/scripts` | core/home/config/nomarchy/default/mako/core.ini,core/home/config/nomarchy-skill/SKILL.md, +3 more | `kept` |  |
+| `nomarchy-update` | `core/system/scripts` | core/home/config/nomarchy/default/mako/core.ini,core/home/config/nomarchy-skill/SKILL.md, +4 more | `kept` |  |
 | `nomarchy-update-available` | `features/scripts/utils` | features/desktop/waybar/config/config.jsonc,features/desktop/waybar/themes/summer-night/config.jsonc | `kept` |  |
 | `nomarchy-update-firmware` | `features/scripts/utils` | features/scripts/utils/nomarchy-menu | `kept` |  |
 | `nomarchy-update-time` | `core/system/scripts` | features/scripts/utils/nomarchy-menu | `kept` |  |