Bridges support

[fmodesto]

Motivation

Add bridge support to NML

Description

• Added Feature 0x06 bridge property mappings in Action0.
• Wired bridge graphics handling into item processing so bridge graphics blocks are collected and emitted through the bridge Action0 path.
• Bridge sprite algorithm step 1: ActionD reserves GRM generic sprites and stores the base in parameter 0x3F.
• Bridge sprite algorithm step 2: ActionA emits the bridge sprite chunks.
• Bridge sprite algorithm step 3: Action6 patches table offsets so references resolve to absolute GRM-based sprite IDs.
• Bridge table output uses prop 0x0D with tables 0-5 for bridge parts and table 6 for bridge ends.

Open Questions

• Should regression tests use proper bridge graphics instead of 1px placeholder sprites?
• Is the current role split (back, front, pillars, head) the right abstraction, or should naming be changed?
• Should we refactor shared item-processing code instead of keeping the current bridge-specific special case?