skeleton: plugin layout + docs, skill/agent migration deferred to iter 1

Establishes the repository structure for the skills plugin:
- README + INSTALL describing the two-layer split (plugin
  mechanics vs per-project profile)
- docs/design, profile-schema, pipeline, agent-template covering
  the universal discipline constants and the profile slot model
- templates/project-profile.yml as a copy-and-fill starting point
- templates/CLAUDE.md.fragment with the baseline orchestrator
  rules a project can import
- install.sh / uninstall.sh wiring skills/ + agents/ into
  ~/.claude/ via idempotent symlinks
- skills/ and agents/ directories empty except for migration
  READMEs; the actual SKILL bodies and agent files migrate
  from ~/dev/ailang/skills/ in the next iteration.

No skill or agent runs yet — this commit only stands up the
structure and documents the substitution model.

uninstall.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+# Uninstall the skills plugin from ~/.claude/.
+#
+# Removes only the symlinks that point into this repo. Other
+# entries under ~/.claude/skills/ and ~/.claude/agents/ are left
+# alone.
+
+set -euo pipefail
+
+REPO_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+unlink_pointing_here() {
+    local dir="$1"
+    [ -d "$dir" ] || return 0
+    for entry in "$dir"/*; do
+        [ -L "$entry" ] || continue
+        target="$(readlink "$entry")"
+        case "$target" in
+            "$REPO_DIR"/*)
+                rm "$entry"
+                echo "removed $entry"
+                ;;
+            *)
+                ;;
+        esac
+    done
+}
+
+unlink_pointing_here "$HOME/.claude/skills"
+unlink_pointing_here "$HOME/.claude/agents"
+
+echo "Uninstall complete."