ci: check the Theia versions our peer range promises

[martin-fleck-at]

The three Theia packages publish a ^1.71.0 peer range while CI installs only 1.75.0, so most of the range we promise adopters is untested.

Legs

• Run the declared floor and latest weekly, plus any version or dist-tag on demand, with fail-fast off so one leg's red cannot cancel the other
• Typecheck and unit-test the framework packages only: no bundler and no e2e, which is where moving Theia drags Electron, React and Node with it

Mechanism

• Pin every @theia/* found across the workspace manifests into the root overrides, then discard the tree; with the lockfile in place npm never re-resolves those edges and the install silently keeps its versions
• Carry a min-version table, because @theia/bundle-plugin published nothing before 1.72.0 and a blanket rewrite 404s the whole install
• Assert every installed @theia/core copy matches, since a partially applied override reads as success from the hoisted path alone
• Pin npm from packageManager, because 10.9.2 crashes in arborist here

Verified by running each step's own body rather than a retyping of it.

• The floor is TRUE: tsc -b, three typecheck:test and 179 tests pass at 1.71.0, and again at 1.75.0
• Control on the assertion: the lockfile-present install succeeds and the assertion rejects it, naming the copy that stayed behind
• Zero copies fails too, which a mismatch-only check would have passed
• Whether the inputs context is simply unpopulated under schedule is reasoned from the docs, not measured; the first cron run settles it