Cardano Updates

Remove -w flag from seq since printf "%02d" already handles padding.
seq -w produced 08/09 which bash treated as invalid octal literals.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Fixes lodash (code injection, prototype pollution), minimatch (ReDoS),
brace-expansion (DoS), tar (path traversal), and @tootallnate/once
(control flow) — reduces audit from 290 to 56 vulnerabilities.
Remaining are unfixable upstream issues in @cardano-sdk/crypto's bundled
npm and eslint@8 transitive deps.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

This is triggered only when the relevant files change. It can also be
run manually.

ci: add weekly flake.lock update workflow

From https://github.com/IntersectMBO/cardano-api at 229dcd4d8668582167e33b64c2b437261e7e6655

Bumps [flatted](https://github.com/WebReflection/flatted) from 3.3.3 to 3.4.2.
- [Commits](https://github.com/WebReflection/flatted/compare/v3.3.3...v3.4.2)

---
updated-dependencies:
- dependency-name: flatted
  dependency-version: 3.4.2
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Bumps [effect](https://github.com/Effect-TS/effect/tree/HEAD/packages/effect) from 3.17.13 to 3.21.0.
- [Release notes](https://github.com/Effect-TS/effect/releases)
- [Changelog](https://github.com/Effect-TS/effect/blob/main/packages/effect/CHANGELOG.md)
- [Commits](https://github.com/Effect-TS/effect/commits/[email protected]/packages/effect)

---
updated-dependencies:
- dependency-name: effect
  dependency-version: 3.21.0
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Bumps [undici](https://github.com/nodejs/undici) from 7.18.2 to 7.24.1.
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](https://github.com/nodejs/undici/compare/v7.18.2...v7.24.1)

---
updated-dependencies:
- dependency-name: undici
  dependency-version: 7.24.1
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

SUBUTXO implementation

The previous Introduction page listed the three components (Consensus,
Storage, Mempool) as separate entities, but this was misleading — in the
code, "Consensus Protocol" does not exist as a distinct component.
Blocks flow directly from the network to ChainDB, and chain selection
lives inside ChainDB, not in a separate protocol layer.

The new System Overview:
- Opens with the consensus problem and why this layer exists
- Adds a C4 Context diagram showing consensus in relation to
cardano-node, the network layer, and the ledger layer
- Names ChainDB (storage + chain selection) and mempool as the main
internal components without implying a separate protocol layer
- Covers era evolution (Byron through Conway) with glossary links
- Describes the code organization: polymorphic core in
ouroboros-consensus vs Cardano instantiations in
ouroboros-consensus-cardano
- Links to existing deeper pages (Design Goals, Data Flow, Ledger
Interaction, Queries, Node Tasks)