Fix Kiira docs snippet issues

[KyleAMathews]

Summary

• fix TypeScript client README snippets so they pass Kiira
• export FetchBackoffAbortError from @electric-sql/client to match documented API
• add Kiira grouping metadata and fix high-signal docs snippets in sync docs

Verification

• npx kiira check --entry packages/typescript-client/README.md --static --raw
• cd packages/typescript-client && pnpm exec tsc -p tsconfig.build.json

Note: package-level pnpm --filter @electric-sql/client typecheck currently fails in this fresh worktree on existing test/dependency typing issues (uuid/pg/fast-check declarations and Vitest mock typings), unrelated to this change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.27%. Comparing base (8bcadb7) to head (010a967).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4526      +/-   ##
==========================================
+ Coverage   69.33%   71.27%   +1.93%     
==========================================
  Files          78       84       +6     
  Lines        9319     9318       -1     
  Branches     2907     2795     -112     
==========================================
+ Hits         6461     6641     +180     
+ Misses       2840     2624     -216     
- Partials       18       53      +35     

Flag	Coverage Δ
packages/agents	?
packages/agents-server	72.90% <ø> (+0.07%)	⬆️
packages/electric-ax	46.42% <ø> (ø)
packages/experimental	87.73% <ø> (?)
packages/react-hooks	86.48% <ø> (?)
packages/typescript-client	91.83% <ø> (?)
packages/y-electric	56.05% <ø> (?)
typescript	71.27% <ø> (+1.93%)	⬆️
unit-tests	71.27% <ø> (+1.93%)	⬆️

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[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@electric-sql/react@4526

npm i https://pkg.pr.new/@electric-sql/client@4526

npm i https://pkg.pr.new/@electric-sql/y-electric@4526

commit: 010a967

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