docs: refresh Perform AGENTS workflow guidance

[mehul0810]

@mehul0810

Learning type

Supersede stale AGENTS snapshot fields and add durable release-cadence workflow guidance.

Evidence

• gh repo view performwp/perform --json nameWithOwner,defaultBranchRef,url shows the default branch is develop.
• git branch --format='%(refname:short)' in the local checkout shows active release branches release/1.6.0, release/1.6.1, and release/1.7.0, so a single hardcoded release branch in AGENTS.md is stale.
• rg -n '^Stable tag:' readme.txt returns Stable tag: 1.6.0, which contradicted the old Current public line: 1.5.1 snapshot.
• gh run list --repo performwp/perform --limit 8 shows current CI activity on release/1.7.0 and on this docs PR, reinforcing that branch and release state changes over time.
• rg -n '30 days|7 days|x\\.9\\.x|cadence checkpoints' /Users/mehulgohil/.codex/automations/perform-daily-issue-triage/automation.toml /Users/mehulgohil/.codex/automations/perform-daily-issue-triage/memory.md shows the active Perform automation already uses explicit 30-day minor, 7-day patch, and major-rollover cadence rules that were not yet preserved in repo docs.

Scope

• Remove the time-sensitive Current public line and Active release branch in this workspace bullets from AGENTS.md.
• Keep the durable branch and release verification guidance for future agents.
• Add repo-specific cadence rules for minor releases, patch releases, pre-major rollover, and live checkpoint verification.

Why AGENTS.md is the durable home

• This is repo-specific branch, release, and cadence workflow policy that future automations need before choosing bases or trusting release timing.
• Leaving it only in automation prompts or memory would allow the same drift to repeat.

What future agents should do differently

• Start workflow-policy and docs PRs from develop unless live release evidence proves a different base.
• Verify release/<milestone> branches, readme.txt, GitHub releases, and WordPress.org state live each run.
• Evaluate release readiness against the 30-day minor cadence, 7-day patch cadence, and pre-major rollover rule, while pulling the active milestone due date live instead of hardcoding dates in AGENTS.md.
• Set PR bases explicitly instead of inheriting GitHub defaults.

Base branch

• Base: develop
• Why: this PR changes durable workflow guidance only, and live repo metadata shows develop is the current integration/default branch.

Validation

• Reviewed the docs-only diff with git diff -- AGENTS.md.
• Ran git diff --check after the AGENTS update.

Rollback or removal notes

• If the repo adopts a different branch model or cadence later, update this section again with live evidence instead of reintroducing fixed snapshot values.

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