fix(deps, frontend): deduplicate Angular toolchain under @angular-builders/custom-webpack

[Musxeto]

What changes were proposed in this PR?

Adds three Yarn resolutions entries to frontend/package.json to force
@angular-builders/custom-webpack's transitive dependencies to the same versions
already pinned in devDependencies:

• @angular-devkit/build-angular → 21.2.19
• @angular/build → 21.2.19
• @ngtools/webpack → 21.2.19

@angular-builders/custom-webpack@21.1.0 declares a loose dep on
@angular-devkit/build-angular: ^21.0.0, which Yarn was resolving to 21.2.18.
This created a nested copy of the toolchain under the builder's own node_modules/
while the pinned 21.2.19 sat unused at the workspace root. Because angular.json
routes both build and serve through @angular-builders/custom-webpack, the
older toolchain (21.2.18) was the one actually compiling the app and running the
dev server — silently, with CI staying green. The same split affected @angular/build
and @ngtools/webpack.

The resolutions field was already in use in frontend/package.json for
monaco-editor, webpack, and jschardet; this PR follows the same pattern.

Result: 276 lines removed from yarn.lock; all three packages now have a single
lockfile entry at 21.2.19; the nested
@angular-builders/custom-webpack/node_modules/@angular-devkit/ copy is gone.

No production source code files were modified.

Any related issues, documentation, discussions?

Closes #8052

How was this PR tested?

Verified the lockfile and installed tree after running yarn install inside frontend/:

# 1. Single lockfile entry per package — no more split at 21.2.18:
grep -n '^"@angular-devkit/build-angular@\|^"@angular/build@\|^"@ngtools/webpack@' \
  frontend/yarn.lock
# 298:"@angular-devkit/build-angular@npm:21.2.19":
# 571:"@angular/build@npm:21.2.19":
# 4294:"@ngtools/webpack@npm:21.2.19":

# 2. No nested @angular-devkit copy under the builder:
ls frontend/node_modules/@angular-builders/custom-webpack/node_modules/
# only `source-map` remains — no @angular-devkit

# 3. Installed version matches the pin:
node -e "console.log(require('./frontend/node_modules/@angular-devkit/build-angular/package.json').version)"
# 21.2.19

Was this PR authored or co-authored using generative AI tooling?

No

[github-actions]

Backport auto-label report

This fix: PR was checked against each actively-supported release branch. release/* labels drive the post-merge backport, so add or remove one to change where this fix lands.

Release branch	Analysis
⚠️ release/v1.3	Not labeled automatically — none of the files this PR modifies exist on this branch (frontend/package.json, frontend/yarn.lock). The fix may target code that isn't on this release, or the files were moved/renamed after the branch was cut. Please check and add release/v1.3 by hand if this fix should be backported here.
✅ release/v1.2	Already labeled — this fix is queued to backport here.

Auto-label run.

[github-actions]

Automated Reviewer Suggestions

Based on the git blame history of the changed files, we recommend the following reviewers:

• Contributors with relevant context: @mengw15
  You can notify them by mentioning @mengw15 in a comment.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.96%. Comparing base (3733b2a) to head (8e4cc6e).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8127      +/-   ##
============================================
+ Coverage     92.94%   92.96%   +0.01%     
- Complexity     4883     4885       +2     
============================================
  Files          1232     1232              
  Lines         51628    51628              
  Branches       6354     6354              
============================================
+ Hits          47988    47994       +6     
+ Misses         2076     2073       -3     
+ Partials       1564     1561       -3     

Flag	Coverage Δ		*Carryforward flag
access-control-service	71.78% <ø> (ø)		Carriedforward from dcf8217
agent-service	99.32% <ø> (ø)		Carriedforward from dcf8217
amber	89.02% <ø> (+0.03%)	⬆️	Carriedforward from dcf8217
computing-unit-managing-service	54.61% <ø> (ø)		Carriedforward from dcf8217
config-service	87.37% <ø> (ø)		Carriedforward from dcf8217
file-service	81.53% <ø> (ø)		Carriedforward from dcf8217
frontend	96.71% <ø> (ø)
notebook-migration-service	83.73% <ø> (ø)		Carriedforward from dcf8217
pyamber	98.47% <ø> (ø)		Carriedforward from dcf8217
workflow-compiling-service	74.09% <ø> (ø)		Carriedforward from dcf8217

*This pull request uses carry forward flags. Click here to find out more.

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[aglinxinyuan]

LGTM!

[Ma77Ball]

@xuang7 and @aglinxinyuan, please fix the CI (rerun it on GitHub UI). It seems related to the time the release label was removed.