docs: inject dartdoc comments into generated public API

[ANAMASGARD]

Summary

Fixes #75 by adding dartdoc comments to the generated public API in lib/bdk.dart via a validated post-generation injection step (Option B).

lib/bdk.dart is produced by uniffi-bindgen and must not be edited by hand. This PR introduces a small Dart injector that reads doc content from scripts/dartdoc/entries.yaml, matches exact declaration anchors in the generated file, and inserts /// comments after every bindings regeneration.

Documented in this PR:

• Core classes: Wallet, Descriptor, Mnemonic, ElectrumClient, EsploraClient, Transaction, Psbt
• Key methods: wallet lifecycle (create / load / persist / dispose), sync (startSyncWithRevealedSpks, applyUpdate), Electrum/Esplora client setup and sync/broadcast, PSBT build/extract flow
• All 30 public exception base types (subclasses deferred for follow-up)

Safety guarantees:

• Exact full-line anchors (not loose regex on class names)
• scope_after for ambiguous symbols like dispose()
• Fails loudly when an anchor is missing or duplicated
• Idempotent re-runs skip anchors that already have docs
• --check mode used in CI to catch drift after bdk-ffi upgrades

Approach

Upstream doc passthrough in uniffi-dart is still open (uniffi-dart#59), so this keeps documentation in-repo and re-applies it automatically from scripts/generate_bindings.sh.

To change docs, edit scripts/dartdoc/entries.yaml and re-run bash ./scripts/generate_bindings.sh — not lib/bdk.dart directly.

Files changed

File	Purpose
scripts/dartdoc/entries.yaml	Doc content map keyed by exact anchors
scripts/inject_dartdocs.dart	Injector with validation and --check
scripts/generate_bindings.sh	Runs injector after uniffi-bindgen
lib/bdk.dart	Regenerated bindings with injected docs
test/dartdoc_injection_test.dart	Verifies anchors and --check pass
justfile	Adds just verify-docs
.github/workflows/ci.yml	Verifies docs after binding generation
CONTRIBUTING.md	Documents the injection workflow

Test plan

• dart scripts/inject_dartdocs.dart --check
• just verify-docs
• dart test test/dartdoc_injection_test.dart
• just analyze
• just test
• just docs — confirm doc/api/ pages for Wallet, Descriptor, Mnemonic are populated

Notes

• Exception subclasses (~100+) are intentionally out of scope for v1; base types document the failure families.
• Happy to coordinate with @as1ndu on follow-up doc wording or additional method coverage.