Patch release for the rendering-helper and scalar-appendix work merged after v0.1.9.

Added

• Added the public treerender package for generic ASCII tree rendering.
  • Provides Render, RenderTree, and RenderTreeWithOptions.
  • Provides DefaultStyle and CompactStyle.
  • Supports wrapping through RenderOptions.WrapWidth.
  • Supports continuation indentation modes including fixed-prefix and anchor-based hanging indentation.
  • Exposes Row.Text, Row.TreePartLines, PrefixMetrics, and related helpers for callers that need stable tree-prefix handling.
• Added the public asciitable package for aligned table and appendix rendering.
  • Provides RenderTable with typed TableSpec and Column definitions.
  • Provides RenderAppendix with typed AppendixSpec definitions.
  • Supports left, right, and center alignment.
  • Preserves multiline table cells without wrapping them unexpectedly.
• Added examples/pgexplainjson, a dependency-free PostgreSQL EXPLAIN (ANALYZE, FORMAT JSON) renderer that demonstrates the generic treerender and asciitable helpers.
  • Supports compact tree output.
  • Supports total-width wrapping.
  • Generates preorder IDs for PostgreSQL plans, which do not provide stable plan-node IDs.
• Added scalar child-link accessors and documentation in plantree.
  • RowWithPredicates.TreePartLines exposes tree prefixes as one line per rendered node-text line.
  • RowWithPredicates.ScalarChildLinks preserves scalar child links in original PlanNode.ChildLinks order.
  • ScalarChildLink carries child index, type, variable, description, and the scalar child node.
  • RowWithPredicates.Keys and RowWithPredicates.ChildLinks remain populated as compatibility mirrors.
• Added scalar appendix controls to cmd/rendertree.
  • --print=predicates,ordering,aggregate selects semantic appendix sections.
  • --print=typed prints all typed scalar links as a raw debug dump.
  • --print=full prints all scalar links, including unnamed links, as a raw debug dump.
  • --print="" suppresses appendix output.
  • --show-vars shows scalar assignment variable names.
  • --resolve-vars resolves direct scalar variable aliases.
  • --resolve-vars-recursive recursively expands scalar variable aliases for investigation.
• Added scalar appendix controls to plantree/reference.
  • Added PrintSection, PrintSections, ParsePrintSection, and ParsePrintSections.
  • Added WithPrintSections, WithShowScalarVars, WithResolveScalarVars, and WithResolveScalarVarsRecursive.
  • Extended RenderConfig with PrintSections, ShowScalarVars, ResolveScalarVars, and ResolveScalarVarsRecursive.
  • RenderConfig.PrintSections distinguishes omitted/null config from an explicit empty list, so JSON [] can intentionally suppress appendices.
• Added the shared internal internal/scalarappendix package used by both cmd/rendertree and plantree/reference.
  • Centralizes scalar appendix parsing, validation, rendering, and scalar variable resolution.
  • Keeps public packages as facades rather than exposing internal symbols.
• Added Gemini review style-guide guidance to avoid readability-reducing micro-optimizations and to treat JSON tags as API design choices.

Changed

• cmd/rendertree now reuses the shared scalar appendix implementation instead of carrying its own separate section parsing and rendering logic.
• plantree/reference now renders appendices through the shared scalar appendix implementation.
• asciitable appendix rendering was generalized beyond predicates through AppendixSpec and RenderAppendix.
• treerender is now public instead of only being available under an internal package.
• The unreleased predicate-specific asciitable compatibility API from the development branch was replaced by the more general appendix API before release.
• treerender hanging-indent validation now requires GetContinuationAnchor only when wrapping is active.
• The golangci-lint GitHub Actions workflow is pinned to a concrete v2 release.
• Local review scratch files are ignored by git.

Fixed

• WithHangingIndent and RenderConfig{HangingIndent: true} no longer fail when no wrap width is configured; without wrapping, hanging indent is a no-op.
• Empty print-section strings now parse as an explicit empty section list, allowing callers to suppress appendix output.
• Scalar appendix JSON config preserves explicit empty printSections slices while still treating omitted/null as the default predicate appendix.

Merged PRs

• #39: feat: expose generic render helpers
• #40: feat: add scalar appendix sections
• #41: refactor: share scalar appendix rendering

Validation

• go test ./...
• mise x -- golangci-lint run --timeout=5m
• git diff --check v0.1.9..origin/main