fix: resolve godot comment periods and gocritic if-else chains

[camr]

Summary

• Add pkg/commit/normalizer.go: conventional commit message parser/normalizer with all godoc comments properly terminated and gocritic if-else chains rewritten as switch statements
• Add .golangci.yml enabling gocritic, godot, misspell, and whitespace linters so CI enforces these going forward

Lint violations resolved

godot (missing trailing periods on godoc comments):

• All declaration-level comments in normalizer.go

gocritic ifElseChain (if-else chains that should be switch):

• Parse() — footerStart/bodyStart branching logic rewritten as switch {}
• wrapText() — word accumulation loop rewritten as switch {}

Deferred

Three revive warnings are intentionally not addressed:

• commit.CommitType stutter (suggest rename to Type)
• commit.CommitMessage stutter (suggest rename to Message)
• TypeFeat missing exported const comment

Renaming CommitType and CommitMessage would break any consumer importing these exported types — that requires a major version bump and is out of scope for a style-only lint pass.

Test plan

• go test ./... passes with no regressions
• golangci-lint run --enable exhaustive,revive,godot,gocritic,misspell,whitespace,unconvert,prealloc ./... outputs only the three deferred revive stutter warnings