chore(deps): upgrade sdk-go to v0.2.0 (credstore API)

[appleboy]

Summary

• Upgrade github.com/go-authgate/sdk-go from pseudo-version to v0.2.0
• Migrate from the old tokenstore package to the new generic credstore package
• Bump Go version from 1.24.2 → 1.25.0 and update transitive dependencies

Changes

File	Change
go.mod / go.sum	Bump sdk-go to v0.2.0; update deps
tui/types.go	Import credstore; update TokenStorage type alias
main.go	Use credstore.Store[credstore.Token]; new store init helpers; updated Save/Load call signatures
main_test.go	Update to credstore API (NewTokenFileStore, Save(id, Token{}))

API differences (v0.1.0 → v0.2.0)

Old (tokenstore)	New (credstore)
Store (concrete)	Store[T any] (generic)
NewFileStore(path)	NewTokenFileStore(path)
NewKeyringStore(svc)	NewTokenKeyringStore(svc)
NewSecureStore(kr, file) + type assertion	DefaultTokenSecureStore(svc, path)
Save(*Token)	Save(clientID string, data Token)
Load(id) (*Token, error)	Load(id) (Token, error)

Test plan

• go build ./... passes
• go test ./... passes (all tests green)

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 42.85714% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
main.go	42.85%	8 Missing ⚠️

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[Copilot]

Pull request overview

Upgrades the AuthGate Go SDK dependency to sdk-go v0.2.0 and migrates the CLI from the legacy tokenstore API to the new generic credstore API for token persistence (including optional keyring-backed storage).

Changes:

• Bump github.com/go-authgate/sdk-go to v0.2.0 and update transitive deps / Go version.
• Replace custom token file JSON + locking with credstore stores and updated Save/Load signatures.
• Introduce -token-store / TOKEN_STORE to select auto|file|keyring storage backend.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
go.mod	Bumps Go version and pins sdk-go v0.2.0 plus new indirect deps for credstore/keyring support.
go.sum	Updates module checksums to match the dependency upgrades.
tui/types.go	Switches TokenStorage to alias the new credstore.Token type.
main.go	Adds credstore-backed token storage (auto/file/keyring) and wires SaveTokens/LoadTokens through the new API.
main_test.go	Updates token persistence tests to use credstore.NewTokenFileStore and new Save/Load signatures.
filelock.go	Removes now-unneeded custom lockfile implementation (replaced by credstore).
filelock_test.go	Removes tests for the deleted lockfile implementation.

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[Copilot]

The new TOKEN_STORE / -token-store configuration is introduced here, but the repo’s user-facing configuration docs/examples (e.g., .env.example and/or README token storage section) don’t mention it. Please update the docs so users can discover and correctly set the new backend selection option.