feat: sltool dte build compiles mission source into a mission file

[vdmkenny]

The compiler step of #1126: mission source back into a standard .DTE, on top of the parser (#1132).

• The compiler (formats/dte/source/compile.zig, and compile/code.zig for the script): declarations in the file's one namespace, each kind's records in the order of its declarations, and code through the statements model. It stops at the first error, with its line and column.
• Object numbers: the shipped missions number objects in the order their authors made them, with gaps, which the source doesn't keep. The compiler numbers the objects last_event names first, since the script names those by a byte (mission 271 needs this), then ships, flight groups and squads.
• Unread data: fields take what most shipped records hold (dte.Ship.blank and the others, which mission 0 now shares), and unread sections stay empty.
• sltool dte build <source> <mission>.
• The round trip (formats/dte/same.zig): the same records and code, decoded, with objects compared by the records the game takes them for. sltool dte check decompiles, builds again, compares and binds. Every mission in the game folder comes back as the same mission.
• Decompiler fixes: objects named by the game's rule (resolveObjects), squad members and formation points as the game walks them, and triggers, squads and formations kept to 100 columns.
• Bridge: each local gets a number, so a local that hides a parameter is told apart from it.
• source.Symbols, the YAML plan's table, had no users and is removed.
• Names where the decompiled missions had numbers: every pilot with a face of its own (pilots 15 and 16 are Ivan and Nicolai Petrov), the deathmatch markers (types 991 to 994), game variables 6 (nicolai_petrov_alive) and 35 (red_dragon_alive), and the environment effects SetEnvironmentFX takes. Scripts see the new pilot, ship type and variable names; make definitions updated the API docs, and multiplayer_list_spawns joins the Ghidra names. A test ties the hand-written pilot names to the generated faces table, so a pilot with a face of its own can't be left without a name.
• One place each: the squad member and formation point walks (dte.zig, used by the engine too), the string pool builder (mission 0 and the compiler), and the command lookup by name (the executor).

Left: mission 0 still fails dte check's byte-exact statements step, as before, because its script is assembled by hand; #610 builds it from source. The .d.luau, the guide and the worked example follow in #1126.

Closes #1136