## Description

Adds workflow-level concurrency controls to all three orchestrator
workflows. This prevents unnecessary parallel runs when multiple commits
are pushed in quick succession and reduces GitHub Actions resource
consumption.

**Changes:**

- Added `concurrency` block to `pr-validation.yml` with
`cancel-in-progress: true` to cancel stale PR validation runs when new
commits arrive
- Added `concurrency` block to `main.yml` with `cancel-in-progress:
false` to prevent cancellation of main branch builds
- Added `concurrency` block to `weekly-security-maintenance.yml` with
`cancel-in-progress: false` for scheduled job protection
- Updated `.cspell/general-technical.txt` with missing dictionary terms
(`carryforward`, `SCHED`, `SECCHECK`) that were causing pre-existing
spell-check failures

## Related Issue(s)

Fixes #274

## Type of Change

Select all that apply:

**Code & Documentation:**

- [ ] Bug fix (non-breaking change fixing an issue)
- [ ] New feature (non-breaking change adding functionality)
- [ ] Breaking change (fix or feature causing existing functionality to
change)
- [ ] Documentation update

**Infrastructure & Configuration:**

- [x] GitHub Actions workflow
- [x] Linting configuration (markdown, PowerShell, etc.)
- [ ] Security configuration
- [ ] DevContainer configuration
- [ ] Dependency update

**AI Artifacts:**

- [ ] Reviewed contribution with `prompt-builder` agent and addressed
all feedback
- [ ] Copilot instructions (`.github/instructions/*.instructions.md`)
- [ ] Copilot prompt (`.github/prompts/*.prompt.md`)
- [ ] Copilot agent (`.github/agents/*.agent.md`)

> **Note for AI Artifact Contributors**:
>
> - **Agents**: Research, indexing/referencing other project (using
standard VS Code GitHub Copilot/MCP tools), planning, and general
implementation agents likely already exist. Review `.github/agents/`
before creating new ones.
> - **Model Versions**: Only contributions targeting the **latest
Anthropic and OpenAI models** will be accepted. Older model versions
(e.g., GPT-3.5, Claude 3) will be rejected.
> - See [Agents Not
Accepted](../docs/contributing/custom-agents.md#agents-not-accepted) and
[Model Version
Requirements](../docs/contributing/ai-artifacts-common.md#model-version-requirements).

**Other:**

- [ ] Script/automation (`.ps1`, `.sh`, `.py`)
- [ ] Other (please describe):

## Sample Prompts (for AI Artifact Contributions)

N/A - This PR does not include AI artifacts.

## Testing

- [x] YAML lint validation passes (`npm run lint:yaml`)
- [x] Spell check passes (`npm run spell-check`)

## Checklist

### Required Checks

- [ ] Documentation is updated (if applicable)
- [x] Files follow existing naming conventions
- [x] Changes are backwards compatible (if applicable)
- [ ] Tests added for new functionality (if applicable)

### AI Artifact Contributions

N/A

### Required Automated Checks

The following validation commands must pass before merging:

- [x] Markdown linting: `npm run lint:md`
- [x] Spell checking: `npm run spell-check`
- [x] Frontmatter validation: `npm run lint:frontmatter`
- [ ] Link validation: `npm run lint:md-links`
- [ ] PowerShell analysis: `npm run lint:ps`

## Security Considerations

- [x] This PR does not contain any sensitive or NDA information
- [ ] Any new dependencies have been reviewed for security issues
- [x] Security-related scripts follow the principle of least privilege

## Additional Notes

### Concurrency Configuration Patterns

| Workflow | Group Key | Cancel In-Progress | Rationale |
|----------|-----------|-------------------|-----------|
| `pr-validation.yml` | `workflow-head_ref` | `true` | Cancel stale PR
runs when new commits arrive |
| `main.yml` | `workflow-ref` | `false` | Protect main branch builds
from cancellation |
| `weekly-security-maintenance.yml` | `workflow` | `false` | Single
weekly job, no ref variation needed |

### Dictionary Updates

Fixed pre-existing spell-check gaps that passed CI due to timing:

- `carryforward` - Codecov configuration term (PR #250)
- `SCHED`, `SECCHECK` - Mermaid diagram labels (PR #252)

⚡ - Generated by Copilot