feat!: migrate to frontend-base

[arbrandes]

Description

This converts the template into an App Repository built on frontend-base: a library that plugs into the Open edX frontend shell, rather than a standalone micro-frontend with its own webpack build. There are breaking changes throughout, and the work was done on a long-lived branch rather than in place, which is why it arrives as one large diff.

Landing it is not a reconciliation. The two branches have diverged across nearly every file, and there is nothing left to merge because the ports from master already happened. The conversion branch takes over instead: legacy-mfe is cut from master's tip first, master is merged into this branch with -s ours to join both histories while keeping the conversion tree, and master then fast-forwards onto the result. openedx/frontend-base#243 has the procedure, settled in OEP-65 ADR 0004. Please do not use the merge button here, which would add a second merge commit and invert the first-parent history the procedure depends on.

The default branch is renamed from master to main immediately before the landing, per #621. This tree already names main in its workflow triggers and documentation links, so they are correct the moment it lands and the new default branch has working push CI from its first commit. The legacy standalone MFE template goes on living on legacy-mfe, which the README points at.

Alongside the conversion, this adds the release setup OEP-10 ADR 0002 defines: a .releaserc naming stable, main and the maintenance branch patterns, and a Release CI workflow that publishes from all of them. Repositories created from this template publish to NPM and are governed by that ADR, but the template shipped neither, so every copy started off the layout it settles on. The workflow's job is gated on the repository name, so this template never publishes and copies need no edit to it. That is the part of openedx/public-engineering#563 that belongs here.

The @openedx/frontend-base peer range also moves from ^1.0.0-alpha to ^1.0.0, and the lockfile from 1.0.0-alpha.39 to 1.0.1 with it, so the template stops demonstrating the library it is built on by depending on an alpha of it.

One deviation from ADR 0004 is deliberate. The ADR has a converted repository annotate openedx.org/release: "legacy-mfe" so release tooling keeps finding the micro-frontend it replaces. This repository already left named releases, its annotation is already null, and no supported release ships it, so null is what it stays. There is nothing for legacy-mfe to be cut for here.

Part of #1029, openedx/frontend-base#243 and #621.

LLM usage notice

Built with assistance from Claude.

[codecov]

Codecov Report

❌ Patch coverage is 30.00000% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 27.27%. Comparing base (c09fccf) to head (7cc13e5).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/routes.tsx	0.00%	7 Missing ⚠️
src/slots/ExampleSlot/ExampleSlot.tsx	0.00%	3 Missing ⚠️
src/slots.tsx	0.00%	2 Missing ⚠️
src/app.ts	0.00%	1 Missing ⚠️
src/widgets/ExampleHeader/app.tsx	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            main     #906       +/-   ##
==========================================
+ Coverage   0.00%   27.27%   +27.27%     
==========================================
  Files          3        9        +6     
  Lines         24       22        -2     
  Branches       0        1        +1     
==========================================
+ Hits           0        6        +6     
+ Misses        24       16        -8     

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[arbrandes]

PR updated for frontend-base 1.0.0 (aka Verawood).