docs: rename plural-agent to erg

[zhubert]

Summary

Updates references from the old "plural-agent" name to "erg" across documentation and the landing page.

Changes

• Update README callout link to point to zhubert.com/erg/ instead of the GitHub repo
• Update landing page HTML: rename comment, link text, and href to erg
• Remove "built on plural-core" tagline from the landing page description

Test plan

• Verify the link in README renders correctly and points to the right URL
• Open docs/index.html locally and confirm the erg callout section displays properly with the correct link

Fixes #317

[zhubert]

Session Transcript

User:
GitHub Issue #317: update docs/index.html

https://github.com/zhubert/plural/issues/317

<user-content type="issue_body">
"plural-agent" was renamed to "erg", so make sure the docs are updated. https://zhubert.com/erg/
</user-content>

---
Approved implementation plan:
<user-content type="approved_plan">
## Implementation Plan: Update docs to replace "plural-agent" with "erg"

### Summary

The tool `plural-agent` was renamed to `erg`. Two files reference the old name and need to be updated.

### Files to Modify

1. **`docs/index.html`** — The "plural-agent callout" section (lines 700–726)
2. **`README.md`** — Line 7, the callout blockquote

### Step-by-Step Changes

#### `docs/index.html`

- Change HTML comment `` → ``
- Change link `href` from `https://github.com/zhubert/plural-agent` → `https://zhubert.com/erg/`
- Change link text from `plural-agent` → `erg`
- Remove the trailing sentence "built on plural-core." from the description (no longer accurate)

#### `README.md`

- Change link text from `plural-agent` → `erg`
- Change link URL from `https://github.com/zhubert/plural-agent` → `https://zhubert.com/erg/`

### Potential Risks / Edge Cases

- No logic changes — purely text/link updates, so risk is minimal.
- The description in `docs/index.html` currently ends with "built on plural-core." — that phrase should be removed since it refers to an old internal package name that no longer applies to `erg`.

### No Questions

The changes are straightforward. Ready to implement once approved.
</user-content>

Assistant:
[ToolSearch: select:Read,Edit]
[Read: index.html]
[Read: README.md]
[Edit: index.html]
[Edit: README.md]
Now let me commit the changes.
[ToolSearch: select:Bash]
[Bash: git add docs/index.html README.md && ...]
Done. Changes committed:

- **`docs/index.html`**: Updated HTML comment, link href, and link text from `plural-agent` → `erg` (pointing to `https://zhubert.com/erg/`), and removed the "built on plural-core." trailing sentence.
- **`README.md`**: Updated the callout link text and URL from `plural-agent` → `erg`.

[Copilot]

Pull request overview

Updates documentation/landing page references to reflect the rename from plural-agent to erg, and adjusts the landing page copy accordingly.

Changes:

• Update README callout to link to https://zhubert.com/erg/ and use the name “erg”.
• Update docs/index.html callout comment/link text/link target to “erg”.
• Remove the “built on plural-core.” tagline from the landing page callout description.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
docs/index.html	Renames the headless-agent callout to “erg”, updates the URL, and removes the “built on plural-core.” tagline.
README.md	Updates the “headless agent” callout name and link target to “erg”.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

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