docs: align README with task-local workflows

[0xth4nh]

What changed?

Updates the root README where the contract-ops reorganization made existing instructions incorrect:

• Replaces deleted setup-* commands with task-directory usage.
• Documents root config/<network>.env files and task-specific .env values.
• Retains a detailed, commented active-task directory tree.
• Preserves and updates the multisig macro tables, helper descriptions, Makefile example, and future-nonce exception.
• Preserves and updates task-origin targets, default variables, path rationale, and mainnet validation requirement.
• Removes only the obsolete walkthroughs for deleted setup templates; task signer READMEs and FACILITATOR.md files are now their source of truth.
• Keeps Markdown prose unwrapped and adds that convention to AGENTS.md.

Checks

signer-tool/node_modules/.bin/prettier README.md --check --prose-wrap never --print-width 150
git diff --check

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/2	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 2 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 2 2 1 if commit is unverified 0 Sum 2

[jackchuma]

We don't need to change the line breaks for badge rows. This seems like unnecessary diff

[leopoldjoy]

PR #785 now documents the active-task lifecycle in AGENTS.md and hardens common verifier address artifacts. Since this PR owns the root README rewrite, please also make these two points explicit in the directory/lifecycle documentation:

• Network-specific deployment addresses live at tasks/<task-id>/config/<network>/addresses.json; task-level records/ remain valid because Foundry separates them by script and chain ID.
• One task directory represents one logical operation across intended network rollouts. Keep it under active/evm/tasks/ and add sibling config/<network>/ directories; run make archive-task only after all currently intended network rollouts are executed or canceled and their final artifacts are committed.

Context: #784 exposed the ambiguity while extending the Nitro validator cutover from Zeronet to Sepolia.

[leopoldjoy]

Follow-up: #785 now directly corrects the overlapping root README active-EVM directory/lifecycle section, including explicit command-line TASK_NETWORK, network-agnostic root facilitator guides, config/<network>/FACILITATOR.md, network-scoped addresses.json, and archive timing. Please rebase #780 on main after #785 lands and retain or reconcile those rules rather than reintroducing the prior shared-Makefile/default-network wording.

[leopoldjoy]

Correction to my earlier lifecycle note: the agreed convention is now one authoritative, network-agnostic task-root FACILITATOR.md with explicit TASK_NETWORK=<network> / config/<network>/ placeholders. Per-network facilitator files should not appear in the standard tree and are discouraged because they duplicate configuration and drift. If an exceptional network has a materially different procedure, use only a linked, delta-only config/<network>/FACILITATOR.md as a last resort. Please preserve this updated wording when rebasing after #785.