v0.8.2 — Prisma importer correctness + JSON defaults

Fixed

• prax-import (Prisma) — @default value round-trip. The Prisma
  importer now emits .prax output that reparses. Three underlying bugs
  were fixed together:
  • String literal defaults (@default("standard")) no longer round-trip
    as doubled quotes (@default(""standard"")). The source quote
    characters are stripped before stashing in AttributeValue::String.
  • Bare-identifier defaults on enum fields (@default(PENDING)) now map
    to AttributeValue::Ident instead of AttributeValue::String. The
    emitter was writing them as quoted string literals, which the parser
    rejected on an enum-typed field.
  • dbgenerated("uuid_to_text(id)") arguments are unquoted the same way
    so they don't double-quote either.
• prax-import (Prisma) — pgvector columns. Prisma models pgvector
  columns via Unsupported("vector(N)"). The importer now recognizes
  the four pgvector shapes (vector(N), halfvec(N), sparsevec(N),
  bit(N)) inside the Unsupported(…) payload and translates them to
  the matching ScalarType::Vector(…) / HalfVector(…) / SparseVector(…)
  / Bit(…) variants. The emitter prints the dimension via the
  @dim(N) attribute that the schema parser already accepts.
• prax validate — diagnostic rendering. The CLI now renders schema
  errors via miette::Report with the source attached, so the specific
  prax::schema::invalid_field, unknown_type, etc. diagnostic is
  visible. Previously every parse or validation failure surfaced as the
  same bare "syntax error in schema" string, which hid the actionable
  detail.
• prax-schema validator — Json default values. The validator now
  accepts String, Array, Boolean, Int, and Float payloads as
  the @default of a Json-typed field. Prisma encodes JSON defaults
  as quoted text literals (@default("[]"), @default("{}")), which
  are valid because Postgres parses the text into jsonb at insert
  time — the old validator only accepted String defaults on
  String-typed fields, rejecting every JSON default outright.

Motivation

Discovered importing the Lexmata schema.prisma (71 models, 33 enums,
1,149 fields, 226 relations) as part of LD-15 / LX-33 — the
admin-backend is adopting Prax as its in-tree ORM and needed a
committable schema.prax regenerated from the authoritative Prisma
schema. The import was failing and the generic "syntax error" message
was masking four distinct bugs; each is now a named regression test.