CLUE-406 chore: replace ts-loader with swc-loader for ~3x faster builds

[scytacki]

Summary

• Replace ts-loader with swc-loader (Rust-based transpiler) for ~3x faster dev builds
• Add ForkTsCheckerWebpackPlugin to run TypeScript type checking in a parallel process
• Configure ESLintPlugin with lintDirtyModulesOnly in dev mode
• Retain ts-loader for CODE_COVERAGE builds (Istanbul instrumentation requires it)

Build performance improvement:

Metric	Before	After	Improvement
Dev initial build	~31s	~10s	3x faster
Core file rebuild	~2.2s	~0.7s	3x faster

Test plan

• Verify npm start works and HMR rebuilds are fast
• Verify TypeScript errors still appear in the browser overlay
• Verify ESLint errors still appear in the browser overlay
• Verify CODE_COVERAGE=true npm start still works (uses ts-loader)
• Verify npm run build succeeds
• Verify npm test passes

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.75%. Comparing base (2aaec63) to head (2113d5e).

❗ There is a different number of reports uploaded between BASE (2aaec63) and HEAD (2113d5e). Click for more details.

HEAD has 24 uploads less than BASE

Flag	BASE (2aaec63)	HEAD (2113d5e)
jest	2	1
cypress-smoke	2	1
cypress-regression	15	0
cypress	7	0

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #2756       +/-   ##
===========================================
- Coverage   86.81%   66.75%   -20.06%     
===========================================
  Files         829      824        -5     
  Lines       44549    44526       -23     
  Branches    11462    11460        -2     
===========================================
- Hits        38673    29723     -8950     
- Misses       5527    13767     +8240     
- Partials      349     1036      +687     

Flag	Coverage Δ
cypress	?
cypress-regression	?
cypress-smoke	43.89% <ø> (-0.27%)	⬇️
jest	49.85% <ø> (ø)

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[cypress]

collaborative-learning    Run #17660

Run Properties:   Passed #17660  •  2113d5e0e3: CLUE-406 chore: replace ts-loader with swc-loader for ~3x faster builds

Project	collaborative-learning
Branch Review	CLUE-406-swc-loader-faster-builds
Run status	Passed #17660
Run duration	02m 58s
Commit	2113d5e0e3: CLUE-406 chore: replace ts-loader with swc-loader for ~3x faster builds
Committer	Scott Cytacki
View all properties for this run ↗︎

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Test results
Failures	0
Flaky	0
Pending	0
Skipped	0
Passing	4
View all changes introduced in this branch ↗︎