[Phase 2] Update ci-standards.md section 9 and the feature-ideation stub comments to the family rule #1211

Story

As a standards maintainer,
I want replace the three claude-opus-4-6 statements in standards/ci-standards.md section 9 with the family rule and reword the stale "Opus 4.6 model selection" comments in the feature-ideation stub template, reconciled with the model mechanism Story 2 verified,
so that the documentation matches the family-default workflow and the actual --model mechanism, with no stale version pins in the docs.

Acceptance Criteria

1. In standards/ci-standards.md the three claude-opus-4-6 statements are replaced with the family rule: the Model table row (L1318), gotcha Add multi-agent isolation strategy using git worktrees #2 (L1394-1396), and the reusable-inputs table row (L1417) now state that the model input defaults to the family opus.
2. Gotcha Add multi-agent isolation strategy using git worktrees #2's substantive point is preserved and reconciled with reality: describe the actual mechanism Story 2 verified (--model ${{ inputs.model }}, CLI-resolved) and, if an ANTHROPIC_MODEL env var is used anywhere, keep the requirement that it be set on the step - but do not document an ANTHROPIC_MODEL: claude-opus-4-6 env var that the workflow does not actually set.
3. The "Opus 4.6 model selection" comments in standards/workflows/feature-ideation.yml (L8 and L23) are reworded to "Opus-family model selection".
4. No synced copies of the stub in consumer repos are hand-edited - only the source-of-truth files in petry-projects/.github change; consumer copies arrive via standards sync.

Tasks / Subtasks

• Rewrite ci-standards.md section 9 lines L1318, L1394-1396 and L1417 to the family rule, cross-referencing the agent-standards.md "Model selection" section from Story 1. (AC: Addressing PR comments #1, Add multi-agent isolation strategy using git worktrees #2)
• Reconcile gotcha Add multi-agent isolation strategy using git worktrees #2 with the mechanism verified in Story 2 (do not document a non-existent ANTHROPIC_MODEL env pin). (AC: Add multi-agent isolation strategy using git worktrees #2)
• Reword the two "Opus 4.6 model selection" comments in standards/workflows/feature-ideation.yml (L8, L23) to "Opus-family model selection". (AC: Add coding standards & principles section to AGENTS.md #3)
• Confirm only source-of-truth files changed; leave consumer-repo synced copies to standards-sync. (AC: Add workflow, environment, and orchestration guidance #4)

Dev Notes

• ci-standards.md is large (~117 KB); all target pins are in section 9 (Feature Ideation). Exact lines: L1318 = the | Model | table row (claude-opus-4-6 set via ANTHROPIC_MODEL env var); L1394-1396 = gotcha Add multi-agent isolation strategy using git worktrees #2 (ANTHROPIC_MODEL: claude-opus-4-6); L1417 = the reusable-inputs | model | row ('claude-opus-4-6').
• IMPORTANT reconciliation: the current reusable sets the model via --model only, not ANTHROPIC_MODEL (verified in Story 2). Write gotcha Add multi-agent isolation strategy using git worktrees #2 to match the real mechanism rather than copying the old ANTHROPIC_MODEL wording; keep the underlying lesson (env vars that ARE set on a step must be set on the step, and family aliases resolve via the CLI, not the raw API).
• standards/workflows/feature-ideation.yml is the thin-caller-stub TEMPLATE that adopting repos copy; its header comments (L8, L23) mention "Opus 4.6 model selection". Only the comments change - do not alter the stub's uses: line, trigger shape, permissions or secrets blocks.
• Testing standard: markdownlint (ci-standards.md) and actionlint (actionlint -ignore 'context' standards/workflows/*.yml) run in ci.yml; keep both clean.
• Depends on Story 2 so the docs describe the verified mechanism (--model vs any env var) instead of guessing.

Project Structure Notes

Doc + comment edits only, in standards/ci-standards.md and the standards/workflows/feature-ideation.yml template. No behavioural code change.

References

• https://github.com/petry-projects/.github/blob/main/standards/ci-standards.md
• https://github.com/petry-projects/.github/blob/main/standards/workflows/feature-ideation.yml
• https://github.com/petry-projects/.github/blob/main/.github/workflows/feature-ideation-reusable.yml
• discussion Standard Proposal: name a model family, never pin a model version #1199

Likely target surface

• petry-projects/.github: standards/ci-standards.md (section 9 rows/gotcha at L1318, L1394-1396, L1417)
• petry-projects/.github: standards/workflows/feature-ideation.yml (comments L8, L23)

Story prepared by the BMAD Scrum Master (Bob) for epic #1208. Status: ready-for-dev.