Rebrand Diffly → Diffr (final Marketplace name)

[MelbourneDeveloper]

TLDR

Rename the entire extension from Diffly to Diffr — the final, Marketplace-accepted name (nimblesite.diffr).

Details

The Marketplace rejected diffly as a name (already taken; public search did not surface it — only publish is authoritative). Diffr published successfully under publisher nimblesite, so this PR makes the whole codebase consistent with that name.

Mechanical, brand-wide rename (Diffly/diffly/DIFFLY → Diffr/diffr/DIFFR) across 38 files:

• Manifest (package.json): name → diffr, displayName → Diffr, all 11 command ids → diffr.*, all menu titles → Diffr: …, menu group prefix → diffr@N.
• Source: scheme SCHEME = "diffr", OUTPUT_CHANNEL_NAME = "Diffr", TITLE_PREFIX = "Diffr:", command/context/memento keys → diffr.*, URI helper symbols (buildDiffrUri, parseDiffrUri, DiffrUriComponents, DiffrAddressableRev, …), provider class DiffrContentProvider.
• File renames: src/providers/DifflyContentProvider.ts → DiffrContentProvider.ts; docs/assets/diffly-icon-* → diffr-icon-*.
• Tests: EXTENSION_ID = "nimblesite.diffr", scheme/URI assertions → diffr://…, E2E env DIFFR_E2E, proposed-api launch arg nimblesite.diffr.
• Pipeline/manifest: release.yml packages/publishes diffr-$VERSION.vsix; shipwright.json id/displayName → Diffr.
• Docs: README, CHANGELOG, CLAUDE.md, Makefile, design-system, plan, spec.

No behavioural change — this is a pure rename. The diffy://-style URI scheme value changes to diffr://, which only matters for in-session diff tabs (not persisted across the rename).

How Do The Automated Tests Prove It Works?

• menus.test.ts asserts package.json contributes.commands/menus are byte-equal to what src/menus.ts generates from the renamed COMMAND_IDS/TITLE_PREFIX, and that the contribSourceControlHistoryItemMenu proposed API is still declared — proving every diffr.* id and Diffr: title is internally consistent.
• uri.test.ts (68 assertions) round-trips buildDiffrUri/parseDiffrUri over diffr://commit/… and diffr://index/… URIs incl. spaces, unicode, #/?, and rejects non-diffr schemes — proving the renamed scheme parses correctly.
• 144 unit tests pass; npm run lint, npm run shipwright:validate, and prettier --check are clean; npm run build reports package.json already in sync.

Spec/Doc Changes

CLAUDE.md, docs/specs/spec.md, docs/plans/plan.md, docs/design-system.md, README.md, CHANGELOG.md all rebranded to Diffr.

Breaking Changes

Yes — the extension identity changes (nimblesite.diffly → nimblesite.diffr) and command ids change (diffly.* → diffr.*). Pre-release only; no published diffly users exist.

⚠️ Reviewer note: repo URLs were rewritten to github.com/Nimblesite/Diffr, but the GitHub repo is currently Nimblesite/Diffly. Either rename the repo to Diffr or revert those URLs to Diffly before publishing — otherwise the Marketplace repo/homepage/bugs links 404.