fix(config): env loader drops falsy values — COCO_VERBOSE=false and friends cannot override lower config layers

[gfargo]

loadEnvConfig discards any parsed env value that is falsy, so boolean env overrides to false never apply. Env vars are the highest-precedence config layer below argv, but they can only turn booleans ON, never OFF. Found in v0.81.0 (main @ 6de37e0).

Failure scenario

• ~/.gitconfig [coco] sets verbose = true (or conventionalCommits = true, includeBranchName = true, openInEditor = true).
• CI job runs COCO_VERBOSE=false coco commit expecting quiet logs → parseEnvValue coerces 'false' to boolean false, then the loader drops it, and the gitconfig true wins. Same for COCO_CONVENTIONAL_COMMITS=false, etc. Documented precedence (env > git config, src/lib/config/utils/loadConfig.ts:45-53) is violated for every boolean-off override.

Root cause

src/lib/config/services/env.ts:88-90:

if (key === 'service' || !envValue) {
  return
}

!envValue was presumably meant to skip empty strings, but after parseEnvValue has already converted 'false' → false (env.ts:225-226) it also drops legitimate boolean false (and would drop a numeric 0 for any future numeric top-level key).

Affected files

• src/lib/config/services/env.ts (defect)
• src/lib/config/utils/loadConfig.ts (precedence contract this breaks)

Suggested fix

Replace the falsy check with an explicit empty check: if (key === 'service' || envValue === undefined || envValue === '') return. parseEnvValue already returns undefined for unset vars, so false/0 flow through and override lower layers as documented.

Testing notes

Existing env tests only assert truthy overrides. Regression test: config layer with verbose: true + process.env.COCO_VERBOSE = 'false' → loadEnvConfig result has verbose === false (and active: true in the returnSource variant).