proven: add missing Zig FFI exports (split from #86, blocks linking)

[hyperpolymath]

Split from #86. This is the mechanical, link-blocking half — separated from the
76 PORT-CHECK marker triage (judgement-heavy work) which remains on #86.

Linking is blocked until this lands: the .afs binding wrappers in
`bindings/affinescript/src/` declare externs against `proven_*` symbols
that aren't yet exported from `ffi/zig/src/main.zig`.

1. Missing Zig FFI exports (highest leverage, blocks linking)

Many extern declarations in the .afs files reference symbols that are
not yet exported from `ffi/zig/src/main.zig` — they were only
reachable via JavaScript FFI scope names in `bindings/javascript/src/`.
Adding the Zig wrappers around the existing Idris implementations
(`src/Proven/Safe*.idr`) unblocks the .afs files from compiling against
the C ABI. Modules confirmed to need new Zig exports (from Batch C / D
reports):

• `proven_header_*` (except has_crlf which exists)
• `proven_lru_*`
• `proven_ml_*` (clamp signature: pick `(x, lo, hi)` or `(lo, hi, value)`)
• `proven_monotonic_*`
• `proven_network_*` (`Ipv4Result` @REPR(C) shape needs Zig struct definition)
• `proven_password_*` (`PasswordValidationResult` @REPR(C) shape)
• `proven_probability_*`
• `proven_queue_*`
• `proven_rate_limiter_*`
• `proven_retry_*` (closure marshalling — see chore(ci): Maximize CI/CD values (Dependabot & Permissions) #2 on parent proven: resolve 76 PORT-CHECK markers (Zig FFI split to #88) #86)
• `proven_state_machine_*`
• `proven_tensor_*`

`proven_unit_` and `proven_version_` are referenced from
`ffi/beam/src/proven_nif.zig` (so the C-ABI shape is confirmed) but
the symbols aren't yet visible in main.zig's export list.

Two specific ABI sign-offs (carried from #86 §4)

• `SafeMath.clamp(lo, hi, value)` vs `SafeMl.clamp(x, lo, hi)` — pick one.
• `Ipv4Result` and `PasswordValidationResult` repr(C) shapes — predicted
  in .afs, needs Zig struct definitions to match.

Acceptance

• All extern declarations in `bindings/affinescript/src/` correspond to a
  Zig export in `ffi/zig/src/main.zig` (verified by building the binding
  against libproven).
• The two ABI sign-offs above are resolved with the chosen shape committed.

Cross-ref: parent #86 (PORT-CHECK marker triage remains there).

[hyperpolymath]

Cross-link: split from #86. The PORT-CHECK marker triage (76 markers across 27 files) remains on #86; this issue tracks only the missing Zig FFI exports (link blocker) and the two ABI sign-offs (clamp arg order, Ipv4Result / PasswordValidationResult repr(C) shapes).