Add CI workflows and fix all golangci-lint violations

Add GitHub Actions PR gates matching the CLI repo pattern:

• ci.yml: tests with -race detection on PRs and push to main
• lint.yml: golangci-lint (60+ linters) with inline PR annotations, gofmt, go mod tidy, and shellcheck checks
• license-check.yml: reusable license compliance from entireio/shared

Add .golangci.yaml with full linter config adapted from CLI, and mise-tasks/lint/ scripts for local development parity.

Fix all 340 existing lint violations across 51 files:

• wrapcheck: wrap external/interface errors with descriptive context
• perfsprint: errors.New for static strings, string concat for Sprintf
• errcheck: handle or explicitly acknowledge error returns
• intrange: modernize for loops to range-over-int (Go 1.22+)
• embeddedstructfieldcheck: separate embedded from regular struct fields
• inamedparam: name interface method parameters
• exhaustive: add missing switch cases
• errorlint: use errors.Is() instead of == for wrapped error checks
• revive: rename unused parameters to _
• goconst: extract repeated string literals into constants
• gocritic: restructure if-else chains and duplicate branches
• noctx: use CommandContext/NewRequestWithContext
• staticcheck: replace nil contexts with t.Context()
• usestdlibvars: use http.MethodGet instead of "GET"