feat: ADR-0035 4d — CREATE [UNIQUE] INDEX / DROP INDEX

Advanced-mode SQL CREATE [UNIQUE] INDEX [IF NOT EXISTS] [<name>] ON
<T> (cols) -> SqlCreateIndex and DROP INDEX [IF EXISTS] <name> ->
SqlDropIndex, both reusing the ADR-0025 executors (do_add_index /
do_drop_index), like 4c reused do_drop_table.

- CREATE UNIQUE INDEX admitted in advanced mode (ADR-0025 Amendment 1):
  ADR-0025 deferred UNIQUE indexes for the simple-mode DSL, but advanced
  mode trusts the user like SQL does. Adds an additive IndexSchema.unique
  flag (project.yaml, serde-default, version stays 1); rebuild re-emits
  CREATE UNIQUE INDEX; the redundant-set guard keys on (columns, unique).
  Simple-mode `add unique index` stays deferred.
- IF [NOT] EXISTS on both forms reuses the 4c no-op-with-note skip
  (journalled, not snapshotted) via CreateIndexOutcome / DropIndexOutcome.
- Unnamed CREATE INDEX auto-named (ADR-0025 convention); the [UNIQUE]
  prefix is a concrete-keyword Choice and the optional name an on-led-first
  selector (the drop-index selector precedent) — trap-safe.
- create/drop each gain a second advanced node; the existing all-candidates
  dispatch handles it (locked by parse tests).
- Unique indexes marked [unique] in the structure view and items panel.
- do_add_index refuses internal __rdbms_* tables as "no such table",
  closing a latent exposure on both the simple `add index` and the new
  SQL CREATE INDEX surfaces (ADR-0025 Amendment 1).

Docs: ADR-0035 status + §13 4d + 4i; ADR-0025 Amendment 1; ADR README;
requirements.md Q1/C3. Plan: docs/plans/20260525-adr-0035-sql-ddl-4d.md.

Tests: 1834 passing / 0 failing / 0 skipped / 1 ignored; clippy clean.

src/dsl/command.rs

@@ -278,6 +278,29 @@ pub enum Command {
     DropIndex {
         selector: IndexSelector,
     },
+    /// Advanced-mode SQL `DROP INDEX [IF EXISTS] <name>` (ADR-0035 §4,
+    /// sub-phase 4d). Name-only (SQL has no positional column form — that
+    /// is the simple `drop index on T(…)`). Executes through the same
+    /// `do_drop_index` machinery as [`Self::DropIndex`]; `if_exists`
+    /// turns an absent index into a no-op-with-note rather than an error.
+    SqlDropIndex {
+        name: String,
+        if_exists: bool,
+    },
+    /// Advanced-mode SQL `CREATE [UNIQUE] INDEX [IF NOT EXISTS] [<name>]
+    /// ON <table> (<col>, …)` (ADR-0035 §4d). Executes through the same
+    /// `do_add_index` machinery as [`Self::AddIndex`] (the columns/
+    /// auto-name reuse), plus the `unique` flag (simple mode has no
+    /// `add unique index` — that stays deferred per ADR-0025). `name` is
+    /// `None` for the unnamed form (auto-named at execution);
+    /// `if_not_exists` makes an existing index name a no-op-with-note.
+    SqlCreateIndex {
+        name: Option<String>,
+        table: String,
+        columns: Vec<String>,
+        unique: bool,
+        if_not_exists: bool,
+    },
     /// Add a column-level constraint to an existing column
     /// (ADR-0029 §2.2). Applied through the rebuild-table
     /// primitive after a §5 dry-run guards populated columns.
@@ -710,6 +733,8 @@ impl Command {
             Self::DropRelationship { .. } => "drop relationship",
             Self::AddIndex { .. } => "add index",
             Self::DropIndex { .. } => "drop index",
+            Self::SqlDropIndex { .. } => "drop index",
+            Self::SqlCreateIndex { .. } => "create index",
             Self::AddConstraint { .. } => "add constraint",
             Self::DropConstraint { .. } => "drop constraint",
             Self::ShowTable { .. } => "show table",
@@ -783,6 +808,11 @@ impl Command {
                 // sensible fallback for logging.
                 IndexSelector::Named { name } => name,
             },
+            // The SQL drop is name-only; the index name identifies it
+            // until the executor resolves the table (mirrors the named
+            // `DropIndex` / `SqlDropTable` fallback).
+            Self::SqlDropIndex { name, .. } => name,
+            Self::SqlCreateIndex { table, .. } => table,
             // Replay isn't tied to a single table; the path is
             // the most identifying thing for log output.
             Self::Replay { path } => path,