docs: add '10 example tasks' gallery to README

[askalf]

Adds a concrete "10 example tasks" section to README.md between What a day looks like and How it works.

Each entry is a single hands run "..." invocation grouped by what the agent leans on (shell-heavy, OS automation, browser/mixed, voice). Examples span Windows + macOS + Linux + voice + non-voice as requested.

Test plan

• README.md only — no code touched, no CI risk.
• Rendered headings + numbered list confirmed locally; section sits naturally between the existing narrative ("What a day looks like") and the architecture deep-dive ("How it works").
• 34-line insertion, zero deletions; git diff --stat confirms no other file touched.

Source ticket: OPS-448B4F40DAD440E0BC5749.