docs: rewrite the README and move customization to its own page

[Haz3-jolt]

Purpose

The README was long, mixed setup detail into the overview, still said the web client did not exist, and referred to roadmap phases. This rewrites it as a README for the product as it is today, with the project badges and the mascot.

Fixes

Fixes #

Approach

• New README: what Axl solves, quick start, how it works, what works today, terminal and web clients, models, sandboxing, extending, building a client, repository map, docs, contributing.
• Project instructions, optional capabilities, prompt templates, themes, and MCP setup move unchanged to docs/customization.md.
• Adds docs/img/axolotl.gif, built from the existing Pink atlas (idle waiting loop, 2x, transparent), and covers it in the existing mascot entry in REUSE.toml. No compatibility or security impact.
• Added a Discord badge alongside the existing ones. Install is from source only, since no release or npm package exists yet.

How was this tested?

• pnpm format:check: passed.
• Viewed the generated GIF frame.
• Not run: reuse lint (not installed locally), link checking, GitHub rendering of the README.

Learning

None.

Checklist

• I reviewed the complete diff.
• I added or updated the smallest relevant test for behavior changes.
• I ran the relevant formatting, lint, type-check, test, boundary, and license checks.
• Every new file has SPDX metadata, directly or through REUSE.toml.
• Every commit has a matching DCO Signed-off-by trailer.
• UI changes include screenshots attached to the pull request, not committed to the repository.

AI assistance

• Generative AI materially assisted this change. Tool and model/version: pi coding agent (model: Claude, version not recorded)
• I manually reviewed, understood, and tested the generated work.

[coderabbitai]

Note

Currently processing new changes in this PR. This may take a few minutes, please wait...

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: 3c32c92b-87a1-4f76-af40-83a9f20e9dda

📥 Commits

Reviewing files that changed from the base of the PR and between 6e22d2d and 14d921e.

⛔ Files ignored due to path filters (1)

• docs/img/axolotl.gif is excluded by !**/*.gif

📒 Files selected for processing (3)

• README.md
• REUSE.toml
• docs/customization.md

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