chore: raise Gemini review threshold (#46)

chore: raise Gemini review threshold (#46)

refactor: share scalar appendix rendering

Summary:
- Move scalar appendix section parsing, validation, rendering, and scalar-variable resolution into a shared internal package.
- Reuse the shared scalar appendix implementation from both `cmd/rendertree` and `plantree/reference`.
- Add public `plantree/reference` appendix controls for section selection, scalar variable display, and direct/recursive scalar variable resolution.
- Preserve explicit empty appendix sections in JSON config while keeping omitted/null config on the default predicates appendix.
- Relax `treerender` hanging-indent validation so anchor callbacks are required only when wrapping is active.
- Add Gemini review style-guide guidance against readability-reducing micro-optimizations and context-free JSON tag suggestions.

Validation:
- `go test ./...`
- `git diff --check origin/main`
- GitHub checks `test` and `lint` passed on `7bc984e8f73019800acbcad81b0b0e032e915f28`.
- Copilot reviewed current HEAD and generated no new comments.
- Gemini reviewed current HEAD and reported no feedback.
- No unresolved review threads, unpublished replies, or pending review drafts remained before merge.

feat: expose all parent links

Summary:
- Add ResolvedParentLink and QueryPlan.ParentLinks(childIndex) to expose every incoming child link for a node.
- Preserve existing GetParentNodeByChildIndex last-parent behavior by keeping the single-parent map unchanged.
- Store and return ResolvedParentLink values so the returned slice does not expose internal wrapper state.
- Add tests for duplicate incoming links, multiple parents, empty/out-of-range lookups, slice isolation, and single-parent compatibility.

Validation:
- go test -v ./...
- git diff --check
- GitHub Actions lint/test passed
- OpenCode diff review with opencode-go/qwen3.6-plus: no material issues
- Copilot current-head review: no new comments
- Gemini value-slice feedback addressed and resolved

docs: add browser and wasm embedding guidance

Add official browser and WebAssembly embedding guidance around the serialization-friendly render config API.

- document plantree/reference as the recommended high-level browser renderer entrypoint
- add a small js/wasm syscall/js example that decodes QueryPlan JSON and returns explicit {output}/{error} results
- harden the wasm example with panic recovery, Uint8Array support, strict config decoding, and a non-js/wasm stub
- update README and package docs with build and usage guidance for browser-facing integrations

Closes #29

fix: keep hanging-indent child guides

Preserve descendant guide lines on wrapped hanging-indent continuation lines, and keep the renderer tests aligned with stable TrimTrailingSpace behavior.

Summary:
- keep a child guide in hanging-indent padding when a wrapped node has descendants
- add treerender and plantree regression coverage for the connected guide behavior
- remove trailing-space-dependent expectations from hanging-indent renderer tests

feat: prefer hanging indent option (#25)

Add WithHangingIndent as the preferred public plantree API, keep the older continuation-indent surface as a deprecated compatibility path, and switch reference and rendertree to the new option.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

feat: add structured custom column flag (#24)

## Summary\n- add repeatable --custom-column flags that accept the same YAML/JSON schema as --custom-file\n- deprecate the delimiter-based --custom syntax while keeping it temporarily for compatibility\n- add a repository Gemini style guide to bias reviews toward correctness and CLI behavior over micro-allocation noise

feat: Add reference implementation (#9)

Add reference implementation for plantree rendering

Implements a reference implementation for rendering Spanner query plans as ASCII tables.

## Features
- Main API: `RenderTreeTable(planNodes, mode, format, wrapWidth)`
- Three render modes: AUTO, PLAN, PROFILE
- Three format styles: TRADITIONAL, CURRENT, COMPACT  
- Configurable text wrapping
- Parse functions for string conversion: `ParseRenderMode`, `ParseFormat`

## Implementation Details
- Validates input (empty planNodes, negative wrapWidth)
- Optimized predicates rendering with direct strings.Builder writes
- Column alignment configuration based on statistics availability
- Comprehensive error handling with context
- Helper functions for predicates detection and column alignments

fix: Fix protoyaml.Marshal to use yaml.UseJSONMarshaler() (#8)