docs(tdd): wire sibling skills to the new entry path

The tdd skill referenced its neighbours (implement, brainstorm,
debug) but none referenced it back. Close the loop so the new
executable-spec-first entry path is reachable and consistent from
every skill that describes a relationship it now belongs to:

- implement: mini-mode trigger + dispatch example now cover a
  RED-first handoff from `debug` OR `tdd` (was debug-only); the
  orchestrator's task template and Phase-3 skip note generalised.
  This was real drift — mini-mode is no longer debug-exclusive.
- planner: skip rule gains the `tdd` case (it skips brainstorm
  AND planner — the RED executable-spec is the plan).
- brainstorm: `tdd` added to the permitted-skip list as the
  profile-gated alternative entry path, plus a cross-ref marking
  brainstorm as the bounce-back target when behaviour stops being
  test-specifiable.
- boss: pipeline diagram, Step-3 routing prose, and cross-refs.
  A test-specifiable feature issue is dispatched to `tdd`
  autonomously, the same way a bug issue goes to `debug`; this is
  NOT a new-cycle bounce-back (the test is the spec). The
  bounce-back fires only reactively, when tdd surfaces a genuine
  design fork.
- debug: reciprocal sibling note + cross-ref (new behaviour is
  tdd's job; debug is for regressions of existing behaviour).

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

boss/SKILL.md

@@ -93,6 +93,8 @@ brainstorm → planner → implement → audit → fieldtest
                   +
                   debug (bug-triggered)
                   +
+                  tdd → implement (mini)  (test-specifiable feature, if profile enables it)
+                  +
                   docwriter (post-stability)
 ```
 
@@ -105,6 +107,21 @@ does `brainstorm` get dispatched. If a spec exists but no plan:
 `audit`. If the iteration is a bug-fix: `debug`. Read each
 skill's `SKILL.md` trigger section if unsure.
 
+If the project profile enables the `tdd` phase and the picked
+item is a **test-specifiable feature issue** — its body pins one
+observable behaviour and the existing-cycle/new-cycle question
+does not apply (it is a backlog issue, not a top-level work
+container needing a fresh spec) — dispatch `tdd` autonomously,
+the same way a bug issue is dispatched to `debug`. `tdd` is its
+sibling: it authors a RED executable-spec and hands the GREEN
+side to `implement` mini-mode. This is **not** a new-cycle
+bounce-back (the test is the spec; no `brainstorm` is dispatched
+to begin). The bounce-back fires only reactively: if `tdd`
+reports the behaviour is not test-specifiable (a genuine design
+fork), that escalation routes to `brainstorm` and — being a new
+cycle that needs a fresh spec — is a bounce-back to the user per
+§"Direction freedom" trigger 4.
+
 If the working tree is mid-flight (uncommitted changes left over
 from a previous session): inspect first, then resume the right
 step. Do not restart from scratch.
@@ -299,4 +316,5 @@ actionable ask, not a wrap-up summary.
   record-reality discipline for the only autonomous glossary writer.
 - **Downstream skills dispatched:** `../brainstorm`,
   `../planner`, `../implement`, `../audit`, `../fieldtest`,
-  `../debug`, `../docwriter`.
+  `../debug`, `../tdd` (test-specifiable feature, profile-gated;
+  autonomously dispatchable like `../debug`), `../docwriter`.