Stabilize JSON stdlib parsing/serialization paths and document v0.9.5 release notes

[Copilot]

Direct JSON usage had regressed in core string/object/unicode paths, and the comprehensive JSON demo had been pared back to avoid those failures. This update restores correct JSON behavior and reinstates full coverage in the JSON standard-library demo.

• Parser correctness (std/json/Json.cod)

  • Reworked parseText() control flow to return deterministically from looped parsing logic instead of falling through to false unterminated text errors.
  • Preserved escape and unicode handling (\", \\, \n, \uXXXX, surrogate pairs) while making failure exits explicit.

• Object map safety (JsonValue)

  • Hardened empty-object paths in set, has, and getKey to avoid invalid iteration/index behavior when object key arrays are empty.
  • Keeps update/lookup semantics intact while preventing edge-case runtime faults.

• Serialization correctness

  • Fixed unicode hex encoding path (hex4) to avoid numeric-type mismatch during escape generation.
  • Corrected text escaping so ordinary characters (notably b/f) are not incorrectly rewritten as control escapes.

• JSON demo coverage restoration

  • Restored full JsonStandardLibraryComprehensive.cod assertions (text, object nesting, round-trip, unicode, invalid cases) using current language keywords/access style.
  • Removed prior temporary reduction that skipped unstable JSON parser paths.

• Release docs

  • Added v0.9.5 changelog entry summarizing JSON stabilization work.
  • Updated README version badge and validation snapshot to current project state.

share parseText() :: value: JsonValue {
    cursor := this.index + 1
    outText := ""
    result := JsonValue.makeError("unterminated text")

    for n of 0 to this.source.length {
        if cursor >= this.source.length { result = JsonValue.makeError("unterminated text") break }
        ch := this.source[cursor]
        cursor = cursor + 1

        if ch == "\"" {
            index = cursor
            result = JsonValue.makeText(outText)
            break
        }
        // escape + unicode handling...
    }

    ~> (result)
}