refactor(packages): dissolve ui/ and rename sdk/ to scaffold/

git mv per the regrouping RFC: the five human-collaboration seams and
tui join packages/interaction/, app-boot becomes packages/boot/, and
jsonrpc joins the renamed scaffold/ (formerly sdk/) as its server half
beside client/protocol/create-sdk/helper/scripts/telemetry, whose
folders drop the legacy sdk- prefix. Three new group README triplets
replace the ui/ and sdk/ ones; tsconfig references/paths/globs,
knip keys, vitest globs, gate scripts, catalogs, docs, and the
lockfile follow. Adds the four settled FIXME rename markers
(dsh-sdk-server, dsh-sdk-telemetry, dsh-sdk-helper, dsh-sdk-scripts).

The scaffold folders diverge from their npm names until those renames
land, so tsconfig.base.json maps the three affected names explicitly
beside the group wildcard. Also repairs two pre-existing stale-path
classes the strengthened sweep surfaced: docs/web-styling.md's retired
web-ui host package and type-model spec fixture-literal joins.

app-boot's three Loader-composition specs time out at the default 5s
under full-suite parallel load on this filesystem (pre-existing;
pass isolated with --testTimeout=30000); interaction/scaffold/boot
suites otherwise green (687 passed).

packages/scaffold/helper/src/documents/env-file.ts

@@ -0,0 +1,111 @@
+/**
+ * Ownership-aware, line-preserving dotenv document.
+ *
+ * @module @deepseek-ai/dsh-helper/documents/env-file
+ */
+
+import { ProjectFile, withTrailingNewline } from './project-file.ts'
+
+interface ParsedVariable {
+  index: number
+  value: string
+}
+
+const VARIABLE = /^(?:export\s+)?([A-Za-z_][A-Za-z0-9_]*)=(.*)$/
+const VARIABLE_NAME = /^[A-Za-z_][A-Za-z0-9_]*$/
+
+/** `.env` appends missing variables; `.env.example` supports managed replacement and removal. */
+export class EnvFile extends ProjectFile {
+  private readonly lines: string[]
+
+  private constructor(relativePath: '.env' | '.env.example', lines: string[], originalText?: string) {
+    super(relativePath, originalText, relativePath === '.env' ? 0o600 : undefined)
+    this.lines = [...lines]
+  }
+
+  /** Create an empty environment file. */
+  static create(relativePath: '.env' | '.env.example'): EnvFile {
+    return new EnvFile(relativePath, [])
+  }
+
+  /** Parse an existing environment file without rewriting unknown lines. */
+  static parse(relativePath: '.env' | '.env.example', text: string): EnvFile {
+    const normalized = text.replace(/\n$/, '')
+    return new EnvFile(relativePath, normalized.length === 0 ? [] : normalized.split('\n'), text)
+  }
+
+  /** Clone the current line model. */
+  override clone(): EnvFile {
+    return new EnvFile(this.relativePath as '.env' | '.env.example', this.lines, this.originalText)
+  }
+
+  private variables(): Map<string, ParsedVariable[]> {
+    const values = new Map<string, ParsedVariable[]>()
+    this.lines.forEach((line, index) => {
+      const match = VARIABLE.exec(line)
+      if (!match) return
+      const name = match[1]
+      const value = match[2]
+      /* v8 ignore next -- both captures are mandatory in VARIABLE */
+      if (name === undefined || value === undefined) return
+      const occurrences = values.get(name) ?? []
+      occurrences.push({ index, value })
+      values.set(name, occurrences)
+    })
+    return values
+  }
+
+  /** Read the effective value; append-only `.env` accepts duplicates and uses the last declaration. */
+  get(name: string): string | undefined {
+    const occurrences = this.variables().get(name) ?? []
+    if (this.relativePath === '.env.example' && occurrences.length > 1) {
+      throw new Error(`${this.relativePath} contains duplicate variable ${name}`)
+    }
+    return occurrences.at(-1)?.value
+  }
+
+  /** Add or replace one SDK-managed `.env.example` variable while preserving unrelated lines. */
+  set(name: string, value: string): void {
+    if (this.relativePath !== '.env.example') throw new Error('.env is append-only')
+    if (!VARIABLE_NAME.test(name)) throw new Error(`invalid environment variable name: ${name}`)
+    const occurrences = this.variables().get(name) ?? []
+    if (occurrences.length > 1) throw new Error(`${this.relativePath} contains duplicate variable ${name}`)
+    const line = `${name}=${value}`
+    if (occurrences[0]) this.lines[occurrences[0].index] = line
+    else this.lines.push(line)
+  }
+
+  /** Append a missing `.env` variable and optional comment without changing any existing declaration. */
+  append(name: string, value: string, comment?: string): boolean {
+    if (this.relativePath !== '.env') throw new Error('.env.example is SDK-managed')
+    if (!VARIABLE_NAME.test(name)) throw new Error(`invalid environment variable name: ${name}`)
+    if (comment !== undefined && (!comment || comment.includes('\n'))) {
+      throw new Error('environment comment must be one non-empty line')
+    }
+    if (this.variables().has(name)) return false
+    if (comment) this.lines.push(`# ${comment}`)
+    this.lines.push(`${name}=${value}`)
+    return true
+  }
+
+  /** Remove one SDK-managed `.env.example` variable while retaining every other line. */
+  remove(name: string): void {
+    if (this.relativePath !== '.env.example') throw new Error('.env is append-only')
+    const occurrences = this.variables().get(name) ?? []
+    if (occurrences.length > 1) throw new Error(`${this.relativePath} contains duplicate variable ${name}`)
+    if (occurrences[0]) this.lines.splice(occurrences[0].index, 1)
+  }
+
+  /** Validate the managed placeholder file; append-only `.env` accepts duplicate declarations. */
+  override validate(): void {
+    if (this.relativePath === '.env') return
+    for (const [name, occurrences] of this.variables()) {
+      if (occurrences.length > 1) throw new Error(`${this.relativePath} contains duplicate variable ${name}`)
+    }
+  }
+
+  /** Serialize all retained lines with one trailing newline. */
+  override serialize(): string {
+    return withTrailingNewline(this.lines.join('\n'))
+  }
+}