docs: overhaul the README, summarise the divergence, prune .env.example

[mfw78]

Two commits. The first adds a divergence summary; the second unwraps it and overhauls the rest of the file, which turned out to be carrying a fair amount of stale and inherited content.

Divergence section

One line per change: order generation, typed errors, structured polling, the fill overlay, the order manifest, handler discovery, proof payload locations, handler validation, and housekeeping. The warning at the top links to it.

It also records that upstream has since added ComposableCowPoller (polling schedules and just-in-time order funding, upstream PRs 122 to 125) and that this tree does not have it. The divergence runs both ways, and a section listing only what was added here would read as a superset of upstream, which is not true.

Corrections

Each was checked against the tree rather than assumed. Ordered by how much damage it could do:

• The TWAP Data struct was missing bytes32 appData. The README told you to ABI-encode that struct as staticInput. Encoding the nine documented fields instead of ten produces the wrong bytes, so the documented recipe could not have worked.
• getTradeableOrderWithSignature was documented as reverting with custom errors. Since feat!: add structured poll interface for watch-towers #23 it does not revert for order conditions at all; it returns a PollResult and reverts only for authorisation and handler-interface failures. Anyone following the README would have wrapped a try/catch around a call that no longer throws, and silently never handled the non-POST verdicts.
• Proof was documented as location 0 or 1 with an opaque payload. Since feat!: URI-based proof payload locations with blob publication verification #39 it is {uris, blobVersionedHashes}, both channels optional, blob hashes verified attached to the setting transaction.
• There are no fork tests. Nothing in test/ calls createSelectFork or reads ETH_RPC_URL, and an unfiltered run gives the same 166 tests as one excluding fork. The three-command ladder documented a distinction that does not exist and an archive node requirement inherited from upstream. Now two commands, verified at 123 unit and 166 with fuzz.
• "Deterministic deployment" described replaying a mainnet creation transaction to reproduce upstream's official addresses, and cited "issue feat!: URI-based proof payload locations with blob publication verification #39" while linking issue 93. This fork has no official addresses to reproduce, so the section is removed rather than repaired. The related "won't deploy to the official addresses" warning goes for the same reason.
• broadcast/deploy_OrderTypes.s.sol/ does not exist. The section now describes what broadcast/ actually holds, which is upstream's records.
• A dangling **TODO** and a link to a [CLI](#CLI) section that has never existed in this file.
• #Conditional-order-cancellation did not resolve, since GitHub slugs are lower-case.
• Environment setup pointed at .env.example wholesale. It now names the variables the scripts actually read: PRIVATE_KEY, SETTLEMENT, SAFE, TWAP, COMPOSABLE_COW, ETHERSCAN_API_KEY.
• Architecture linked only to a HackMD page predating this work, and now points at docs/architecture.md, docs/discovery.md and docs/design/.
• deploy_ExtensibleFallbackHandler and deploy_ValueFactories exist but were undocumented.
• ```solidity= is a HackMD directive GitHub does not recognise as a language tag.

.env.example

Third commit. Roughly half the file configured upstream's watch-tower rather than anything here: Tenderly node URLs and credentials, a NETWORK selector defaulting to Goerli, BLOCK_NUMBER and STORAGE for replaying a block in WATCH mode, a Slack webhook, a Sentry DSN. Eleven variables, none read by any script, test or workflow in this repository, so copying it to .env mostly produced settings with nothing to act on them.

What remains is annotated with its consumer. Checked both directions: every retained variable has real references, every removed one had zero.

ETH_RPC_URL also no longer defaults to http://erigon.dappnode:8545, a host specific to whoever wrote the file, which fails in a way that looks like a broken script rather than an unset variable.

Checking

• Every relative link target resolves; both anchors match a real heading.
• Both documented test commands were run: 123 and 166.
• generateOrder is declared inside interface IConditionalOrderGenerator, and no getTradeableOrder remains in src/.
• Zero-amount guards resolve to OrderNotValid(ZeroAmount.selector) in GoodAfterTime, StopLoss, TradeAboveThreshold and TWAP.
• "Shape-compatible" settlement path rests on isValidSafeSignature being signature-identical to upstream/main, diffed directly. That is the claim most worth challenging in review, since it is what a reader would lean on when judging how much of an existing integration survives.

README only. forge fmt --check clean.