docs: enrich OOM-fix streaming-refactor plan + gitignore fix

Adds the comprehensive implementation plan for fixing the
`codeiq enrich` OOM at ~/projects/ scale (49k files / 434k nodes,
exit 137 on 15 GB host).

Plan structure: 4 phases (Quick wins -> TreeCursor -> Streaming
three-pass refactor -> Verification harness), 12 tasks total, each
shippable as one PR. Includes a ralph-loop execution recipe so the
loop can drive the plan to completion without human gates inside
each phase.

Research backing the plan:
- Empirical pprof on airflow (9,151 files): 91% allocations from
  tree-sitter.(*Tree).cachedNode, peak RSS 3.8 GB
- Trajectory: istio 1.1 GB / airflow 3.8 GB / ~/projects ~9-15 GB
- Code walk: GraphBuilder dedup maps never released after Snapshot;
  ServiceDetector emits 434k CONTAINS edges
- Kuzu defaults: 80% of system RAM for buffer pool, no streaming
  Appender API in v0.7.1-v0.11.3 (issue #2739)
- ETL patterns: ID-only dedup + compact NodeIndex for linkers
  (drops Properties/Annotations) fits ~35 MB at scale

Completion criterion (from plan):
  /usr/bin/time -v codeiq enrich ~/projects/
must complete with peak RSS < 4 GiB, exit 0, populated graph.

Also fixes the .gitignore quirk that was preventing
`docs/superpowers/plans/*.md` from being trackable:
`docs/superpowers/*` ignored the plans/ directory itself, so the
later `!docs/superpowers/plans/*.md` negation couldn't take effect.
Added `!docs/superpowers/plans/` to un-ignore the directory first.

Author: aksOps

.gitignore

@@ -107,4 +107,9 @@ docs/superpowers/baselines/**/raw/**
 # Agent-generated plans / scratch (not project deliverables)
 phase*-plan.md
 *-plan.md
+# …but project-deliverable plans land under docs/superpowers/plans/ and
+# must be trackable. The directory itself needs un-ignoring first because
+# the outer `docs/superpowers/*` rule above excludes the dir, and an
+# ignored directory's contents cannot be re-included by a later pattern.
+!docs/superpowers/plans/
 !docs/superpowers/plans/*.md