fix(data): remove 18 fabricated placeholder values from PDA records

[Seungpyo1007]

What

Follow-up to the PDA dedup pass (#335). That pass only caught fabricated import
placeholders inside duplicate pairs (where comparing the two sides revealed the
fake one). This scans all 112 post-dedup pda records for the same
fabricated-default fingerprint — a single fake-precise value repeated across many
unrelated devices — regardless of whether a record had a twin.

Fixed 18 records; documented the rest that can't be repaired without inventing.

Both gates pass:

• python -m app.validate → passed
• integrity_check.py <data> --strict → 0 hard anomalies

Clusters found

Field	Value	Count	Verdict
ram_gb	1	83 / 112	fabricated — no PDA 2000-2011 had 1 GB RAM
battery_mah	1500	33	fabricated (classic-Palm cluster) but unfixable — see below
display.ppi	114	26	real — 240x320 QVGA on 3.5" really is ~114 ppi
display	3.5" / 240x320	26	real — QVGA was the ubiquitous PDA screen
weight_g	190	9	real — iPAQ h63xx chassis family + i-mate HTC rebrands

Spot-checked against sources: Dell Axim X5 = 32/64 MB (Wikipedia, PCMag,
DigitalTrends), Palm IIIc = 8 MB (Wikipedia, TidBITS, Computing History) — all
flatly contradict the stamped ram_gb=1.

Fixed (18 records, all cited — ram_gb is required so repaired, not nulled)

• 13 Dell Axim — Wikipedia Dell Axim specification table. X5/X3/X30 low-end
  ("Basic") = 32 MB (0.03125); X3/X3i Advanced, X30 Advanced, and the entire
  X50/X51 line = 64 MB (0.0625).
• 5 Fujitsu-Siemens Pocket Loox N520/N560 = 64 MB (0.0625) — Fujitsu N520
  user manual + clubic N560 launch spec.

No value invented — every figure comes from an authoritative source added to
source_urls.

Left as-is, documented (not guessed, not nulled)

• Classic Palm line (Palm IIIc/IIIxe/VIIx = 8 MB, m100 = 2 MB, m105/m125/m130/
  m500/m505 = 8 MB, m515 = 16 MB, Tungsten/Zire/Treo/Centro …): their real RAM is
  below the schema's ram_gb >= 0.016 (16 MB) floor, so it cannot be
  represented — almost certainly why they were stamped with ram=1 on import.
  Can't set the true value (fails validate), can't null a required field.
• Other ram_gb=1 records (i-mate PDA phones, HP iPAQ Glisten, Mitac Mio 728,
  later Palm Treo/webOS) need individual per-device sourcing; left documented
  rather than risk inventing.
• battery_mah=1500: the classic Palms ran on AAA/AA cells (m100/m105/m125 —
  no mAh rating) or small internal Li-ions; there is no clean per-device mAh to
  cite without inventing, and the field is required (can't null).
• ppi=114, the 3.5"/240x320 combo, and weight_g=190 are genuinely shared
  real values, not fabricated defaults — left untouched.

Ownership / dump

data/pda/ only. Dump refreshed as the last commit (fresh scratch DB,
TECHAPI_DATA_DIR on this worktree): only the 18 repaired detail pages change,
no other collection touched.

Closes #296 — this removes a sourced slice of the pda fabricated-placeholder values;
the required-field-but-unrepresentable/unsourceable remainder stays open and is
documented above.