chore: reconcile on-client path + add golangci-lint config (R13+R14)

R13 — on-client path reconciliation:
- AGENTS.md: 6 occurrences of /opt/homelab-context/ → /opt/homelab/
  (sections 1, 2, 5, 7)
- .agents/NOMOS.md: 2 occurrences of /opt/homelab-context/ → /opt/homelab/
- CLIENTS.md already used /opt/homelab/ — now consistent across all docs.
  The repo is still named 'homelab-context' (git remote), it just clones
  to /opt/homelab/ on enrolled clients per CLIENTS.md.

R14 — golangci-lint/staticcheck/govulncheck tooling:
- .golangci.yml (new): config enabling govet, staticcheck, ineffassign,
  unused, errcheck, gosimple, typecheck, misspell, revive. Excludes
  generated code (internal/httpapi/gen/, internal/db/sqlcgen/) and
  relaxes errcheck in test files.
- Makefile: split 'lint' target into vet, golangci, govulncheck subtargets.
  Each checks if the tool is installed and prints install instructions
  if not. 'make lint' runs all three.
- CI already had golangci-lint-action + govulncheck (both advisory);
  the action auto-discovers .golangci.yml.

.golangci.yml

@@ -0,0 +1,41 @@
+# golangci-lint configuration for Oikos
+# Docs: https://golangci-lint.run/usage/configuration/
+run:
+  timeout: 5m
+  tests: true
+
+linters:
+  enable:
+    - govet        # go vet
+    - staticcheck  # advanced static analysis
+    - ineffassign  # detect ineffectual assignments
+    - unused       # find unused identifiers
+    - errcheck     # check for unchecked errors
+    - gosimple     # simplifications
+    - typecheck    # standard type checking
+    - misspell     # find commonly misspelled English words in comments
+    - revive       # fast, configurable linter (replaces golint)
+
+linters-settings:
+  errcheck:
+    # Allow unchecked errors on common Close/Flush patterns (deferred cleanup)
+    exclude-functions:
+      - (io.Closer).Close
+      - (*os.File).Close
+
+issues:
+  # Exclude generated code
+  exclude-rules:
+    - path: _test\.go
+      linters:
+        - errcheck
+    - path: internal/httpapi/gen/
+      linters:
+        - all
+    - path: internal/db/sqlcgen/
+      linters:
+        - all
+  # Don't auto-exclude common patterns
+  exclude-use-default: false
+  max-issues-per-linter: 0
+  max-same-issues: 0