feat(fieldtest): bundle findings into collective issues; document the harvest sweep

Encode the tracker-growth practice ratified in the aura field run:

- fieldtest/SKILL.md — tracker filing defaults to bundling: one
  collective issue per fieldtest for related friction/spec_gap
  findings, consolidate-before-filing ahead of ANY new issue,
  per-issue filing only for real bugs (low-severity may wait in
  the collective issue). The fieldtester's per-finding report is
  unchanged; this is an orchestrator-side filing rule.
- docs/pipeline.md — new § Harvest sweep: the recognised batch
  shape for draining settled single-issue backlog (issue bodies
  as spec source, sequential implementer batches of 2-3, one
  non-removable independent whole-diff review, audit close,
  compact fieldtest under its normal skip rules). Registered as
  the specify/planner exception under § Skip rules.
- specify/SKILL.md, planner/SKILL.md — codify the sweep as a
  named alternative / skip case, per "skipping is codified per
  skill, not ad hoc".
- docs/conventions.md — register the noun in § Vocabulary.

closes #36

specify/SKILL.md

@@ -35,6 +35,8 @@ the decision as a *source* rather than making it inline.
 
 `specify` is a core pipeline node: it is the gate before `planner` on
 every design path that is not a bug fix or a test-specifiable feature.
+The side paths that carry no fresh prose design — `compiler-driven`,
+the harvest sweep — bypass it (`../docs/pipeline.md` § Skip rules).
 Where `tdd` is one entry path among three (chosen when behaviour is
 test-specifiable), `specify` sits on every prose-design path — it is
 not bypassed for those.
@@ -59,6 +61,9 @@ Triggers:
 - An observed bug — use `debug` directly (RED-first).
 - A tidy iteration — use `audit` directly.
 - A trivial mechanical edit — per the project's CLAUDE.md carve-out.
+- Settled single-issue backlog drained as a batch — the harvest
+  sweep's issue bodies are the ratified spec source; no new spec is
+  written. See `../docs/pipeline.md` § Harvest sweep.
 
 **Skipping a gate is never permitted.** The interview is `brainstorm`'s,
 and its absence here is the whole point — but the *production gates*