feat(template): derive ErrorTemplate from proto Template option

[yordis]

• Lets services declare their error contract once in proto and pick it up in Go without hand-rewriting the same domain/reason/code/visibility/help/metadata in two places.
• Field-level FieldOptions (visibility, value/default_value) drive per-instance metadata, so a populated proto message becomes a fully-formed error without per-call boilerplate.

[cursor]

PR Summary

Medium Risk
Adds protobuf-reflection-based template construction and metadata derivation, which changes how errors can be generated and introduces new dependencies/tooling for codegen. Main risk is correctness/compatibility of proto option parsing and derived metadata behavior across message types.

Overview
Adds NewErrorTemplateFromProto and ErrorTemplate.FromProto to construct templates from protobuf message-level template options and derive per-instance metadata from annotated fields (including fixed-value and default-value policies).

Extends ErrorTemplate/NewError creation to carry template metadata into produced errors, and adds comprehensive examples/tests plus proto + generated Go testdata to validate behavior.

Updates repo tooling: introduces buf.gen.yaml and buf module config/lock for test protos, adds a CI job to ensure generated code is committed, and bumps Go to 1.26 with new trogonproto/protobuf dependencies.

^{Reviewed by Cursor Bugbot for commit 6191c3f. Bugbot is set up for automated code reviews on this repo. Configure here.}

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: f4045977-8ba8-49a2-b5ce-ace95091500b

📥 Commits

Reviewing files that changed from the base of the PR and between 2679893 and 6191c3f.

⛔ Files ignored due to path filters (3)

• go.sum is excluded by !**/*.sum
• internal/testdata/gen/trogonerror/testdata/v1/errors.pb.go is excluded by !**/*.pb.go, !**/gen/**
• internal/testdata/proto/buf.lock is excluded by !**/*.lock

📒 Files selected for processing (10)

• .gitattributes
• .github/workflows/ci.yml
• buf.gen.yaml
• error.go
• example_test.go
• go.mod
• internal/testdata/proto/buf.yaml
• internal/testdata/proto/trogonerror/testdata/v1/errors.proto
• template_proto.go
• template_proto_test.go

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch yordis/feat-template-from-proto

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