[CLI] Migrate collections, discussions, extensions, endpoints and webhooks to `out singleton

[hanouticelina]

Part of #3979 (Phase 2)

This PR migrates list and info commands in collections , discussions, extensions, endpoints and webhooks to use the out singleton.

This PR introduces some notable breaking changes,in addition to those that affects all migrated commands, e.g. -q/--quiet replaced by --format quiet:

hf endpoints ls: (same issue as for hf auth whoami)

• JSON: flat fields only (name, model, status, task, framework, instance, vendor, region), it was full endpoint.raw with nested objects when passing --format json.

hf discussions info:

• Rich text view replaced by JSON output
• --comments, --diff, --no-color flags removed

---

Note

Medium Risk
Changes CLI output formatting and flags across multiple commands (notably replacing --quiet/-q with --format quiet and altering hf discussions info output/flags), which can break scripts relying on previous text output or options.

Overview
Migrates collections, discussions, extensions, endpoints, and webhooks commands to use the out singleton (--format [agent|auto|human|json|quiet]) instead of ad-hoc print/print_list_output + --quiet/-q.

Updates output behavior to be mode-aware (human tables vs agent TSV/JSON), adds per-invocation reset of output state (HFCliApp.__call__ / hf callback), and adjusts some commands’ structured output (e.g., hf discussions info now emits JSON via out.dict and drops --comments/--diff/--no-color; hf endpoints ls/hf webhooks ls preserve nested fields in json/agent but flatten for human display). Docs and tests are updated to match the new flags and output semantics, including safeguards that quiet mode doesn’t leak between CLI invocations.

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[bot-ci-comment]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[hanouticelina]

breaking change here: the rich text view defined in _print_discussion_info is replaced by out.dict(details), consistent with all other info commands (models info, datasets info etc). The --comments, --diff, and --no-color flags are removed. Comments and diff are always included in the JSON output. I think it's fine no? a user can just call hf discussions diff to view diffs separately

[cursor]

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