test(sdd): wire test-sdd-workspace.sh into the runner; note git clean -fdx

The per-worktree workspace test was added but never registered in
run-skill-tests.sh, so it only ran when invoked by hand. Add it to the
fast unit-test array alongside the other pure-shell test.

Also document, in the Durable Progress section, that the ledger now
lives in git-ignored working-tree scratch, so `git clean -fdx` deletes
it — recover from `git log` if that happens.

skills/subagent-driven-development/SKILL.md

@@ -260,6 +260,8 @@ a ledger file, not only in todos.
 - The ledger is your recovery map: the commits it names exist in git even
   when your context no longer remembers creating them. After compaction,
   trust the ledger and `git log` over your own recollection.
+- `git clean -fdx` will destroy the ledger (it's git-ignored scratch); if
+  that happens, recover from `git log`.
 
 ## Prompt Templates
 

tests/claude-code/run-skill-tests.sh

@@ -74,6 +74,7 @@ done
 # List of skill tests to run (fast unit tests)
 tests=(
     "test-worktree-path-policy.sh"
+    "test-sdd-workspace.sh"
     "test-subagent-driven-development.sh"
 )