docs: put Sepolia in scope and write down the provider flag exception (closes #165)

The README's 1.0 non-goal said Ethereum mainnet only, while Sepolia
ships as a selectable network. It now puts mainnet and Sepolia in scope
and other chains out of it.

The injected provider's flag named after the other wallet stays, as an
interface-compatibility flag many dApps check. It is now written down
as an exception to the rule against naming competitors, in the README's
Policies section and in RULES.md, and the comment beside it says so.
Neither document spells the name, so script/check-censored, which
already allows the flag only in src/content/inpage.js and its built
copies, is unchanged.

Model: opus-5-5

TODO.md

@@ -44,6 +44,16 @@ then continue tagging as milestones land.
 
 # Completed Steps
 
+- 2026-10-07: Two contradictions between the documents and the code are resolved
+  as ruled on [#165](https://git.eeqj.de/sneak/AutistMask/issues/165). The
+  README's 1.0 non-goal now puts Ethereum mainnet and the Sepolia testnet in
+  scope and other chains out of it. The injected provider's flag named after the
+  other wallet stays, as an interface-compatibility flag many dApps check, and
+  is written down as an exception to the rule against naming competitors in the
+  README's Policies section, in `RULES.md` and in a comment beside it in
+  `src/content/inpage.js`. `script/check-censored` already allows that flag only
+  in that file and its built copies, so it is unchanged.
+
 - 2026-10-07: Two holes in what `tests/persistedFieldContract.test.js` checks
   are closed ([#379](https://git.eeqj.de/sneak/AutistMask/issues/379)). The
   check that every swept field is driven both truthy and falsy counts only