docs: a runnable example for named merge slots and graph inputs

[psyinf]

Adds apps/namedPipeline, one example app for the features of #15 and #16. Following the one-app-per-theme convention, the named-slot and named-input examples move there from apps/textPipeline.

The app shows

• named slots: (after: reversed, before: upper) -> Compare, matched by name
• slot checks: a misspelled slot name ("did you mean") and the slot it leaves unfed
• several named inputs: push() for one, filter(GraphInputs{}.set(…).set(…)) for both, and the errors thrown for an unknown key or a mistyped value
• input checks: a misspelled in.<key> against GraphInputs::of, reported at build time
• both together: two named inputs meeting in a lambda merge with named slots (registerTypedMergeFilter with names), holes filled with defaults
• toMermaid, labelling the merge's edges with the slot names

Docs

• EXAMPLE.md: new section 10; the Named slots and Several named inputs subsections move there from sections 4 and 5, which keep a one-line pointer; sample table, run commands and full outputs updated
• README: sample list and run commands
• CHANGELOG: entry under Unreleased

Not included: the "done" paragraph in TODO.md still lists only the stateful and composite apps; it will be updated with the pending TODO.md edits.

Built with the windows-msvc-debug-developer-mode preset, no warnings; namedPipeline and textPipeline output matches EXAMPLE.md.