test: add Angular version test matrix (toolchain swap-in-place)

[JuroUhlar]

What

Adds a CI workflow that verifies the library builds and its unit tests pass against every supported Angular major (15–21).

This is a simpler alternative to the scaffolding approach in #85. Instead of generating a fresh Angular workspace per version, it keeps the committed workspace (angular.json, tsconfig*, jest config) and just swaps the installed Angular toolchain, then runs the existing ng build + jest.

How

A single matrix job. The only per-version knowledge is the compatibility table in matrix.include (Node / TypeScript / zone.js / jest-preset-angular), which is intrinsic to Angular's own support policy:

• Pin toolchain — pnpm add the version-matched @angular/*, ng-packagr, typescript, zone.js, jest-preset-angular.
• Build — ng build fingerprintjs-pro-angular (catches ng-packagr / compiler-cli breakage).
• Test — pnpm test (the existing jest suite; catches runtime/API breakage).

Footprint

3 files: .github/workflows/test-matrix.yml, .node-version, and an engines field in package.json.

Scope / known trade-off

This covers library build + unit tests across 15–21. It does not exercise each version's freshly generated project scaffolding, nor does it compile a real consumer app against the published package. A follow-up can add a consumer-build job (build the SDK to dist, then compile committed per-version demo apps against it) to close that gap — kept out of this PR to keep the first step minimal.

Draft: version pins in the matrix table may need a nudge on first CI run; that tuning is data in one table, not logic.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Fpy8yBUra4yxpMp5F9Xm7a

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Generated by Claude Code

[github-actions]

⚠️ This PR doesn't contain any changesets. If there are user-facing changes, don't forget to run:

pnpm exec changeset

to create a changeset.

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	75%	30/40
🟡	Branches	60%	3/5
🟢	Functions	83.33%	5/6
🟡	Lines	72.97%	27/37

Test suite run success

10 tests passing in 2 suites.

Report generated by 🧪jest coverage report action from ef10927

Show full coverage report

St	File	% Stmts	% Branch	% Funcs	% Lines	Uncovered Line #s
🟡	All files	75	60	83.33	72.97
🔴	src	0	100	100	0
🔴	public-api.ts	0	100	100	0	5-13
🟢	src/lib	93.33	60	100	92.59
🟢	fingerprint.module.ts	100	100	100	100
🟢	fingerprint.providers.ts	100	100	100	100
🟢	fingerprint.service.ts	89.47	60	100	88.88	57,64
🟢	version.ts	100	100	100	100
🟡	src/lib/tokens	66.66	100	0	66.66
🟡	fingerprint-angular-settings-token.ts	66.66	100	0	66.66	7