feat(pipeline): route to the lightest correct methodology; move execution loops onto the Workflow substrate

The selector forced every task through the heaviest methodology's
critical path: a behaviour-preserving, type-enumerable change paid the
same specify -> planner -> implement front-half as a novel feature,
because it was neither new behaviour (tdd) nor an observed bug (debug)
and so fell to specify by elimination. Two coupled defects — a selector
with no verification axis, and an all-or-nothing executor — kept the
existing lighter path unreachable and uneconomical. This fixes both.

Part A — verification-keyed selector (boss/SKILL.md):
- Replace the three-way "design line" with an ordered cascade that adds
  a verification/enumeration axis ahead of the settled-vs-fork question.
  Each lighter arm carries a positive trigger matched by signature, not
  reached by elimination.
- New `compiler-driven` arm: a type/signature edit at a definition site
  that propagates mechanically. Observe-then-bounce — make the edit,
  build, run the suite; clean build AND suite green unchanged commits;
  a hole bounces up (specify for a design choice, tdd for discovered
  test-specifiable new behaviour); a regression bounces to debug.
- The observed-bug RED-first gate is first in the cascade, so a
  mechanical-looking fix cannot bypass it.
- The straddle rule ("add an enum variant") is codified as a rule:
  mechanical/forwarding -> compiler-driven; encodes new behaviour ->
  tdd/spec; doubt routes up.
- The executor is the elevated inline carve-out plus a shipped workflow,
  not a heavy new skill ("the largest concrete win is small").

Part B — Workflow substrate (implement/workflows/):
- implement-loop.js: the per-task loop as a deterministic script. Each
  phase (implementer -> spec-compliance -> quality, + tester for E2E) is
  a separate top-level agent() call, so a single phase is independently
  invokable and inter-phase aggregation/re-loop is code. Retires the
  implement-orchestrator agent's inline-role-switch workaround (the four
  phase agents survive as the agent-types the script dispatches).
- compiler-driven-edit.js: the observe-then-bounce loop.
- install.sh / uninstall.sh symlink shipped workflows into
  ~/.claude/workflows/.
- specify and brainstorm stay prose + interactive (human-intent oracle);
  only the autonomous/mechanical loops moved. try-and-error is deferred.

Docs (pipeline taxonomy, design, agent-template, migration, README) and
all selector<->executor cross-references updated; the arm and its
executor are co-located so a future re-route through the full loop is a
visible regression.

Verified by an adversarial multi-agent pass: PASS on all six acceptance
criteria; two coherence concerns fixed. The shipped scripts are
syntax-validated but exercised only in a downstream target project (the
skills repo is not itself a pipeline target).

closes #7

specify/SKILL.md

@@ -434,7 +434,7 @@ CLAUDE.md project facts):
 
      **Re-loop limit: ≤ 2 self-correction rounds. The 3rd unresolved
      editorial `BLOCK` escalates** — same shape as the per-task re-loop
-     limit in `implement-orchestrator`.
+     limit in the implement loop (`../implement/workflows/implement-loop.js`).
 
   Three properties keep this loop honest, not a way to grind the panel
   into submission: