Add WithTransformerFunc helper and improve docs discoverability

[asadijabar]

What

Add an ergonomic inline transformer registration helper and improve discoverability of related configuration features in the docs/examples.

This PR:

• adds Loader.WithTransformerFunc(fn func(context.Context, *T) error) as a convenience wrapper over WithTransformer(TransformerFunc[T](fn))
• adds a focused unit test for the new helper in loader_test.go
• documents WithTransformerFunc(...) and preferred inline usage in docs/api-reference.md
• updates the transformer example in README.md and examples/transformer/main.go to use the shorter syntax
• improves README/docs navigation and anchors for common user paths (watch/reload status, common paths, deep-linkable quick-start sections)

Why

Inline typed transformers are a common use case, and the current syntax is verbose at call sites:

• WithTransformer(rigging.TransformerFunc[T](func(...) ...))

The helper keeps the existing transformer API and semantics intact while making the common inline case easier to read and copy from docs/examples.

The docs changes make features like transforms, snapshots, watch/reload, and key-mapping semantics easier to discover from the README and quick-start pages.

Type

• Fix
• Feature
• Docs
• Performance
• Breaking change

Testing

Executed:

gofmt -w loader.go loader_test.go
gofmt -w examples/transformer/main.go
go test ./...

Result:

• go test ./... passed (including compile checks for examples/basic and examples/transformer)

Would run:

go vet ./...
make ci

Reason:

• extra static/CI parity checks; not required to validate this additive helper and docs/example updates locally

Checklist

• Tests pass (go test ./...)
• Formatted (gofmt -s -w .)
• No vet warnings (go vet ./...)
• Coverage maintained (>70%)
• Added tests if needed
• Updated docs if needed

Notes:

• Formatted changed Go files with gofmt -w (not repo-wide gofmt -s -w .)
• Coverage was not measured in this change

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For reviewers: Does this align with Rigging's philosophy of simplicity and zero dependencies?

[Copilot]

Pull request overview

This PR adds a convenience helper WithTransformerFunc to reduce verbosity when registering inline transformers, and significantly improves documentation discoverability through strategic anchor additions and navigation tables.

Changes:

• Adds Loader.WithTransformerFunc(fn func(context.Context, *T) error) as an ergonomic wrapper around the verbose WithTransformer(TransformerFunc[T](fn)) syntax
• Updates transformer examples in README.md and examples/transformer/main.go to use the new concise syntax
• Enhances documentation navigation with deep-linkable anchors in quick-start.md and configuration-sources.md, plus comprehensive navigation tables in README.md

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
loader.go	Adds WithTransformerFunc convenience method that delegates to WithTransformer
loader_test.go	Adds comprehensive unit test verifying chaining, registration, and execution of the wrapped transformer
examples/transformer/main.go	Updates example to use the new WithTransformerFunc helper instead of verbose WithTransformer(TransformerFunc[...]) syntax
docs/api-reference.md	Documents the new helper with example usage and recommends it for inline transforms
docs/quick-start.md	Adds HTML anchors for deep-linking and standardizes heading capitalization
docs/configuration-sources.md	Adds HTML anchors for improved documentation navigation
README.md	Updates transformer example to use new helper and adds comprehensive navigation tables linking to documentation sections with new anchors

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