docs: docs/agents/project-planning/README.md missing Network ISA-95 Planner agent

## Component

Documentation

## Bug Description

The `docs/agents/project-planning/README.md` Agent Overview table and Getting Started table do not include the **Network ISA-95 Planner** agent (`network-isa95-planner.agent.md`) that was added to the `project-planning` collection in commit `636912f` (PR #1177).

The README currently lists five agents in its overview table:

| Agent | Sub-Category | ... |
|---|---|---|
| BRD Builder | Requirements | ... |
| PRD Builder | Requirements | ... |
| ADR Creation Coach | Architecture | ... |
| Arch Diagram Builder | Architecture | ... |
| Security Planner | Security | ... |

The Network ISA-95 Planner is absent from both this table and the Getting Started scenario table, leaving users unable to discover the agent through the documentation.

## Expected Behavior

`docs/agents/project-planning/README.md` should include the Network ISA-95 Planner in:

1. **Agent Overview table** — add a row describing the agent's sub-category (Networking/OT Security), workflow type, persistence, and key output (ISA-95 zone/conduit map and remediation roadmap).
2. **Getting Started table** — add a scenario row for brownfield/greenfield ISA-95 network segmentation reviews.
3. **A dedicated section** (similar to Requirements, Architecture, Security) describing the agent's intake requirements, zone-conduit model, and remediation roadmap output.

Note: the agent carries `maturity: experimental` in the collection manifest, so the documentation should flag it accordingly.

## Steps to Reproduce

1. Open `docs/agents/project-planning/README.md`.
2. Search for "ISA-95", "network-isa95-planner", or "Network ISA-95 Planner" — no results found.
3. Compare against `collections/project-planning.collection.yml`, which lists `.github/agents/project-planning/network-isa95-planner.agent.md`.

## Additional Context

- **Changed code file:** `.github/agents/project-planning/network-isa95-planner.agent.md` (added in PR #1177, commit `636912f`)
- **Documentation file needing update:** `docs/agents/project-planning/README.md`
- **Collection manifest:** `collections/project-planning.collection.yml` — agent is listed with `maturity: experimental`
- Agent description: "ISA-95-aligned network planning assistant for secure edge Kubernetes to Azure connectivity, remediation roadmaps, and beginner-friendly guidance"

> Generated by [Documentation Update Check](https://github.com/microsoft/hve-core/actions/runs/24854250462/agentic_workflow) · ● 2.3M · [◷](https://github.com/search?q=repo%3Amicrosoft%2Fhve-core+is%3Aissue+%22gh-aw-workflow-call-id%3A+microsoft%2Fhve-core%2Fdoc-update-check%22&type=issues)

Start with docs/agents/project-planning/README.md and compare it with collections/project-planning.collection.yml and .github/agents/project-planning/network-isa95-planner.agent.md. Update the Agent Overview and Getting Started tables, add the dedicated ISA-95 section, and flag the agent as experimental; done means all three documentation areas describe the agent consistently.

Written by the indexing model from the issue text.