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

fieldtest/SKILL.md

@@ -165,6 +165,30 @@ The orchestrator drives downstream:
 
 `fieldtest` does NOT self-resolve.
 
+**Tracker filing — bundle by default.** A fieldtest typically
+yields more findings than a cycle closes issues (3-5 vs 1-2 in
+the field evidence on issue #36), so filing each finding as its
+own issue grows the tracker structurally with every fieldtested
+cycle. When findings are filed onto the tracker rather than
+routed inline:
+
+- Consolidate before filing: before creating **any** new issue,
+  check whether an open issue on the same line of work can
+  carry the scope — absorb via a comment there instead.
+- Related `friction` / `spec_gap` findings of one fieldtest go
+  into **one collective issue**, not one issue per finding.
+- A real `bug` keeps its own issue — it is a forward-queue work
+  item. A low-severity bug may wait in the collective issue
+  instead.
+- The fieldtester's report stays per-finding — classification
+  is the agent's contract and does not change. Bundling is this
+  orchestrator-side filing rule only. The writes themselves
+  follow `../issue/SKILL.md`, as every tracker write does.
+
+When settled single-issue items accumulate anyway, the
+orchestrator drains them as a **harvest sweep** — the batch
+shape defined in `../docs/pipeline.md` § Harvest sweep.
+
 ## Cross-references
 
 - **Agent dispatched:** `agents/fieldtester.md` — carries the
@@ -176,6 +200,9 @@ The orchestrator drives downstream:
 - **Closing gate it feeds:** `../docs/pipeline.md`
   § Milestone-close gate — the milestone fieldtest's green
   roll-up is the functional leg of that gate.
+- **Batch drain it feeds:** `../docs/pipeline.md`
+  § Harvest sweep — the batch shape that drains accumulated
+  settled single-issue items (bundled findings included).
 - **Cadence ordering:** fieldtest runs *before*
   `../docwriter/SKILL.md`; docwriter happens at a later,
   longer stability window.