feat(decisions): implement agents plan tree CLI command

Add CHANGELOG and CONTRIBUTORS entries for the agents plan tree
CLI command implementation (issue #8525). The command was implemented
as part of the v3 plan lifecycle decision tree visualization feature,
providing hierarchical tree rendering with multiple output formats,
superseded decision filtering, depth limiting, and per-type ordinal
labeling.

ISSUES CLOSED: #8525

CHANGELOG.md

@@ -16,6 +16,17 @@ The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ### Added
 
+- **`agents plan tree` CLI Command** (#8525): Implemented the `agents plan tree <plan_id>`
+  command for visualizing decision trees in the v3 plan lifecycle. The command renders a
+  hierarchical tree of all decisions for a given plan with support for multiple output
+  formats (`rich`, `plain`, `json`, `yaml`, `table`). Features include: per-type ordinal
+  labeling for clear node identification, superseded decision filtering with `--show-superseded`
+  flag, depth limiting via `--depth`, graceful handling of empty decision trees, and a
+  'Decision IDs (for correction)' panel for easy reference. BFS tree traversal uses
+  `collections.deque` for correctness. Comprehensive Behave unit tests in
+  `features/plan_explain.feature` and CLI coverage tests in
+  `features/plan_explain_cli_coverage.feature` achieve >=97% coverage.
+
 - **Architecture Pool Supervisor Milestone Assignment** (#7521): Added a "PR Workflow
   for Major Changes" section to the `architecture-pool-supervisor` agent definition
   documenting the milestone assignment step for spec PRs. The agent now has

CONTRIBUTORS.md

@@ -25,3 +25,4 @@ Below are some of the specific details of various contributions.
 * HAL 9000 has contributed automated bug fixes, CLI output formatting improvements, and ongoing maintenance as part of the CleverAgents automation system.
 * HAL 9000 has contributed the file edit encoding parameter fix (PR #8258 / issue #7559).
 * HAL 9000 has contributed the architecture-pool-supervisor milestone assignment feature (PR #8188 / issue #7521): added `forgejo_update_pull_request` permission and documented the PR workflow for major spec changes, enabling automatic milestone assignment for specification PRs.
+* HAL 9000 has contributed the `agents plan tree` CLI command implementation (PR #8691 / issue #8525): implemented the decision tree visualization command with hierarchical tree rendering, multiple output formats, superseded decision filtering, depth limiting, and per-type ordinal labeling for the v3 plan lifecycle.