Fix 124 pre-existing lint issues in legacy code

[renecannao]

Lint Cleanup

The codebase has 124 pre-existing lint issues detected by golangci-lint v2. Currently CI uses `only-new-issues: true` to avoid blocking PRs.

Breakdown

• errcheck: 50 — unchecked error returns
• staticcheck: 50 — various static analysis findings
• unused: 12 — unused functions, variables, struct fields
• ineffassign: 10 — ineffectual assignments
• govet: 2 — copies lock value

Approach

Fix incrementally by package, one PR per package:

1. `go/inst/` — largest package, most issues
2. `go/logic/` — recovery logic
3. `go/http/` — API handlers
4. `go/kv/` — consul/zk stores
5. Others

Once all fixed, remove `only-new-issues: true` from CI so lint enforces on all code.

[renecannao]

Fixed in PR #60 — reduced from 124 to 39 issues (68% reduction). Remaining 39 are ST1006 (legacy receiver naming).