worldname — promote the survey placeholder namer to a real package with codas and onset clusters

[philoserf]

internal/survey/survey.go carries an unexported placeholder namer (its own comment: "T5 has no name generator, so this supplies a placeholder until one exists") producing strict CVCV names (Ropoze, Tibaki).

Scope

• Promote to internal/worldname with an exported Generate(r *dice.Roller) string; survey draws from it.
• Adopt ../traveller-worldgen/worldname/worldname.go's fragment tables: onset clusters (br, dr, ...), vowel digraphs (ae, ia, ou, ei), and a coda table (th, rn, ss, ld, ne) with their 2-3 syllable + final-coda structure — this is what turns Ropoze into Peimern/Draejapu.
• Draw via t5's dice.Index(n), NOT their (d6-1)*6+(d6-1) mod len trick — that is unbiased only while every table length divides 36, and silently biases the day a fragment is added.
• Mind dice-stream impact: survey names consume draws, so this shifts seeded sector output — regenerate the README pinned sample block per the standing rule (systemgen: GenerateForMap and Generate diverge in dice consumption, so one seed gives two different systems #321).

Since names are invented content (no book table), no golden-from-worked-example applies; a determinism test + shape assertions suffice.