fix(motd): remove legacy /usr/libexec/mios/motd + /usr/lib/profile.d/mios-motd.sh

Per operator directive: "legacy is now deprecated and should be
streamlined into the current codebase and then removed after
consolidation". The MOTD/dashboard system has had two coexisting
implementations since v0.2.0 -- the legacy pair (motd binary +
profile.d trigger) and the canonical pair (mios-dashboard.sh +
zz-mios-motd.sh). Now consolidating to the canonical pair only.

What's removed
──────────────

usr/lib/profile.d/mios-motd.sh
   Legacy profile.d trigger that called fastfetch + the legacy
   /usr/libexec/mios/motd renderer. Only fired if /usr/lib/profile.d/
   was sourced by /etc/profile (NOT standard on Fedora -- typically
   only /etc/profile.d/ is sourced). Even when it did fire, it
   duplicated zz-mios-motd.sh's work without any "shown once" guard,
   re-flooding the operator with banner+fastfetch+motd inside every
   tmux pane / SSH session. Pure dead weight on a deployed host;
   active duplication on MiOS-DEV (where overlay-builder.sh copies
   both into /etc/profile.d/).

usr/libexec/mios/motd
   Legacy ~7 KB MOTD renderer. Older approach: own ANSI escape
   sequences, own banner, own dashboard layout, no tty0/console
   degradation, no frame, no ticker. Superseded by
   /usr/libexec/mios/mios-dashboard.sh (16 KB) which renders inside
   an 80-column frame with proper tty0 fallback, consolidates
   fastfetch via --services-only mode, supports --no-color /
   --no-frame / --ticker, and is the declared canonical entry point
   per its docstring + per zz-mios-motd.sh + per /usr/bin/mios-dash.

What's kept (canonical chain)
─────────────────────────────

/etc/profile.d/zz-mios-motd.sh
   Profile.d trigger. zz- prefix sorts last, runs after mios-env.sh.
   Gated on PS1 set + TTY + dedup ($MIOS_MOTD_SHOWN) + skips inside
   tmux/screen. Calls mios-dashboard.sh.

/usr/libexec/mios/mios-dashboard.sh
   Canonical renderer. Frame + ASCII art + fastfetch + services
   block + loop hint. Read by /etc/profile.d/zz-mios-motd.sh on
   interactive shell login + by /usr/bin/mios-dash for manual
   refresh + by mios-dashboard-issue.service to render to
   /etc/issue.d/ for the pre-login banner.

/usr/bin/mios-dash
   Operator-facing wrapper. `mios-dash` from any shell triggers
   the canonical dashboard render.

What's updated (cosmetic)
─────────────────────────

tools/lib/install-env.ps1
   Comment in /etc/mios/install.env referenced the legacy
   /usr/libexec/mios/motd path. Updated to point at
   /usr/libexec/mios/mios-dashboard.sh.

Net effect for the operator
───────────────────────────
- One MOTD path instead of two. No duplication, no race-to-render,
  no ambiguity about "which file do I edit to change the banner."
- Slightly slimmer image (-7.7 KB legacy renderer + the 412-byte
  legacy trigger).
- The SSH-into-MiOS-DEV path now renders the canonical dashboard
  exactly once, matching what a deployed MiOS host shows. Manifesto
  alignment: "the unified installation dashboard is visible and
  enhanced with the mios dash showing the banner/header ascii art,
  the fastfetch stats, the mios motd stats" -- this is now THE
  rendering chain.

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

Author: Kabuki94

tools/lib/install-env.ps1

@@ -38,7 +38,7 @@ function Write-MiosInstallEnv {
     # ever appear in the hash, so the wrap is safe.
     $lines = @(
         "# /etc/mios/install.env -- written by the 'MiOS' Windows installer.",
-        "# Read by /usr/libexec/mios/wsl-firstboot, /usr/libexec/mios/motd,",
+        "# Read by /usr/libexec/mios/wsl-firstboot, /usr/libexec/mios/mios-dashboard.sh,",
         "# and /usr/libexec/mios/forge-firstboot.sh.",
         "# Vendor defaults: /usr/share/mios/env.defaults",
         "MIOS_USER=$User",