chore: consolidate Dependabot dependency updates

[mantzas]

Summary

Consolidates all open Dependabot PRs into a single update:

• Update Dockerfile: golang 1.25 → 1.26
• Update .github/workflows/ci.yml: upload-artifact v6 → v7
• Note: go-redis PR Bump github.com/redis/go-redis/v9 from 9.17.1 to 9.17.2 #380 is obsolete (master already at v9.17.3, newer than Dependabot's v9.17.2)

Supersedes

• Bump actions/upload-artifact from 6 to 7 #385, Bump golang from 1.25 to 1.26 #386
• Bump github.com/redis/go-redis/v9 from 9.17.1 to 9.17.2 #380 (obsolete — master already has newer version)

All changes are dependency version bumps only — no code logic changes.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 52.78%. Comparing base (d1a503e) to head (5ef5e04).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/sh/sh.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #390   +/-   ##
=======================================
  Coverage   52.78%   52.78%           
=======================================
  Files          24       24           
  Lines         934      934           
=======================================
  Hits          493      493           
  Misses        383      383           
  Partials       58       58           

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