fix(gstack): link spec skill, complete gitignore allowlist (BLK-007)

A gstack submodule bump added `spec` (v1.47) and the iOS device-farm
5-skill set (v1.43) but gstack `./setup` was never re-run, leaving all 6
as source-only — unlinked, invisible to Claude and untouched by
reset/`gstack on`.

  - Link `spec` only, surgically: skills/spec/SKILL.md symlink matching
    gstack setup's per-skill pattern (real dir + absolute SKILL.md link).
    Platform-agnostic, useful planning skill. Added to full + web-full
    profiles (must be in the active `full` profile or `set full` would
    re-disable it).
  - iOS skills deliberately NOT linked: this is a Linux host, and the iOS
    device-farm needs a Mac daemon + Tailscale + physical iOS devices.
    Linking them would add 5 dead skills plus passive token cost.
  - Complete the .gitignore gstack allowlist: add the 12 entries missing
    from it — `spec`, the 5 `ios-*` (so they stay ignored if a future
    setup on a Mac materializes them), and 6 already-parked skills
    (document-generate, landing-report, scrape, setup-gbrain, skillify,
    sync-gbrain). The parked ones matter because `gstack on` moves parked
    skills into skills/, where any allowlist gap becomes untracked git
    noise. Also drop the stale `skills/checkpoint` entry (renamed to
    context-save).

Verified: `profile show full`/`web-full` report spec enabled; the
source-vs-allowlist drift check is now empty; profile.sh still parses.

The gstack submodule pointer bump itself is left uncommitted (separate
pending work).

Memory: BLK-007 -> resolved; LRN-025 (gitignore allowlist must cover all
toggleable skills incl. parked, else enabling one = git noise).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -8,7 +8,6 @@ skills/benchmark
 skills/browse
 skills/canary
 skills/careful
-skills/checkpoint
 skills/codex
 skills/connect-chrome
 skills/cso
@@ -45,6 +44,21 @@ skills/context-restore
 skills/context-save
 skills/make-pdf
 skills/plan-tune
+skills/spec
+skills/document-generate
+skills/landing-report
+skills/scrape
+skills/setup-gbrain
+skills/skillify
+skills/sync-gbrain
+# iOS device-farm skills (need a Mac daemon + Tailscale + iOS devices) —
+# not linked on this Linux host; ignored so they stay out of git if a
+# future gstack setup on a Mac host materializes the symlinks.
+skills/ios-clean
+skills/ios-design-review
+skills/ios-fix
+skills/ios-qa
+skills/ios-sync
 
 # External skill symlinks — auto-created by link.sh
 skills/emil-design-eng