feat: configure output flags via environment variables

[liiight]

Summary

Closes #2872.

Adds environment-variable equivalents for the output-related flags so grouped output can be enabled once at the CI/job level (a single variables: entry) instead of being repeated on every task invocation or set unconditionally via the Taskfile output: key:

Flag	Env var
--output	TASK_OUTPUT
--output-group-begin	TASK_OUTPUT_GROUP_BEGIN
--output-group-end	TASK_OUTPUT_GROUP_END
--output-group-error-only	TASK_OUTPUT_GROUP_ERROR_ONLY

These are wired through the existing getConfig helper (the same mechanism used by TASK_VERBOSE, TASK_COLOR, etc.), so the usual precedence applies: CLI flag > env var > default. An explicit CLI flag still overrides the env var via pflag's Changed tracking.

Changes

• internal/flags/flags.go: source the four output flag defaults from TASK_* env vars.
• internal/flags/flags_test.go: unit tests for each env var, fallback-to-default, invalid-bool handling, and env > taskrc-config precedence.
• website/src/docs/reference/environment.md + cli.md: document the new env vars and cross-link them from the flags.
• CHANGELOG.md: Unreleased entry.

Testing

• go build ./... and go vet ./... pass.
• go test ./internal/... passes (new flags tests included).
• Verified end-to-end with a built binary:
  • TASK_OUTPUT=group enables grouping
  • TASK_OUTPUT_GROUP_BEGIN/END apply templates
  • CLI flag overrides the env var
  • validation still rejects begin/end without --output=group

[trulede]

The changes look good. Mods normally update the changelog themselves.

Comment: recently envars were added for (only) CLI options which are also present in the task config schema. For CI (non-interactive) use cases some other envars might be useful:

• status
• watch
• parallel
• exit-code
• dir
• taskfile
• interval
• global
• force
• force-all

[liiight]

I'll remove the changelog changes.
Regarding the other option you suggested, would you like me to add them as part of this MR as well? I'd be happy to

[trulede]

I'll remove the changelog changes. Regarding the other option you suggested, would you like me to add them as part of this MR as well? I'd be happy to

Lets see what the mods say. I just noted it when reviewing the change.

[liiight]

Gentle bump. I would greatly appreciate your time and eyes on this MR.
Thanks in advance 🙏

[vmaerten]

I'll take a look tomorrow