Serialize any links network to links-notation text (full LiNo round-trip)

[konard]

Context

Issue #47 requires "storage (presenting as links notation (text based as in
https://github.com/link-foundation/links-notation) ...)". LiNo parses in
(src/lino_parser.rs), but arbitrary networks cannot be written back out as
links-notation text - only self_description_text emits LiNo-style lines. See
requirements.md R-7 and
solution-plans.md S-5.

The reference Rust parser is the links-notation crate 0.13.0 (verified on
crates.io 2026-06-10), which formal-ai also pins
(formats-storage-apis.md Part B).

Scope

• Implement LinkNetwork::to_lino() and LinkNetwork::from_lino() covering
  every link kind (references, names, metadata) so any network round-trips.
• Property test: from_lino(to_lino(n)) is isomorphic to n across parsed
  and hand-built networks.
• Align the emitted dialect with the links-notation 0.13 crate so other
  ecosystem parsers can consume the output; record divergences as parity
  fixtures.
• Use a doublets-style id discipline for unnamed links so text and (future)
  binary storage share one addressing scheme.

Acceptance criteria

• to_lino/from_lino round-trip property test passes on language
  fixtures and synthetic networks.
• Output of to_lino is accepted by the links-notation crate parser in
  a test.
• links-notation PARITY_FIXTURES gain a serialization (output-side)
  fixture, not just parse-side.
• Changelog fragment added (bump: minor).

References

• Requirement: requirements.md R-7
• Solution: solution-plans.md S-5
• Part of We need to carefully compare all competitors in all scopes with out project, and make sure we have the richest features set #47; work lands on branch issue-47-76af108c0f24 (PR Finish issue #47 parity feature set #48).

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Filed from docs/case-studies/issue-47/proposed-issues/05-lino-network-serialization.md. Part of the implementation plan for #47.