Awesome project, happy to see this being developed in a way that looks this polished and professional!
Are you planning to make this into a paid service (Noticed a few references to it being Free), i.e. this becoming a commercial venture rather than a hobby project?

Just signed up and noticed a few things. Many minor things, just listing what I noticed. Absolutely not criticism either - like I said, very glad to see something like this being built - so this is just to aim at improving even further.

1. The privacy policy refers to a 'local mode', I'm assuming this is the Demo? The demo mentions clearing the demo-data through settings, but once you do that you will exit the demo application. Re-entering and all demo data is back.
2. Happy to see that you didn't take the route of scraping account stats from the FB website. Some other 'award miles tracking' websites do this and I personally strongly oppose that method as it breaches various terms&conditions, and it introduces a huge security hole regarding credentials storage.
3. Having said that - the flying blue PDF export contains a bunch of personal data: Names, account info, etc. While I fully understand why, especially if this is a hobby project, the privacy/about pages do not instantly make me feel comfortable sharing those details. What happens to the uploaded PDFs, which data is extracted and is the original pdf kept or deleted? Is it ever stored on disk or remains in application memory at all times?
4. Some of these may be unreasonable to ask for a hobby project, but because this looks so well done and professional - Planning on adding GDPR compliance?

From a functionality perspective, some things I noticed:

1. It would be nice to have the signup form classify the password field in such way that the browser will suggest a new (random) password (Chrome does this, but it may require some kind of attribute on the password field). Nitpicking but still
2. To reduce uploading sensitive data, any plans on allowing flight imports by copy/pasting flight activity from the FB/KL/AF websites? Potentially a copy/paste from the PDF omitting privacy-sensitive items that should not be needed for the process?
3. Alternatively many people use TripIt for tracking their flights. They have an API allowing to fetch flight history and details. Will not include miles or XP data - but will include flight segments, city pairs, cabin, fare code, pricing. The challenge is that Tripit data is notoriously incomplete - not all fields may always be populated. Format for some are also somewhat undefined (e.g. fare could be "W Economy", "WLGHTKL", "Economy" or "Economy Light". An import could be a good starting off point for manual addition, though.
4. The miles value is calculated using 1.2 cent per mile. Could that be done on the calculated redemption value, or if that data is unavailable, a cpm defined by the user?
5. Manually inputting flights does not yet keep track of non-existing cabins. E.g. LIM-AMS-ATH in PE classifies the AMS-ATH segment as 10XP while the service would be Economy (5XP). I'm not sure if there is a reliable dataset to determine which international routes do or do not have Premium cabins available, possibly historical data from other members if the dataset is large enough? The same would apply to trips in LaPremiere where some of the segments would be in Business.
6. Most likely it won't really be possible to determine the actual cabin flown with 100% certainty. Sometimes the cabin exists but is full, and therefore the pax booked into another cabin (This happens a lot on short haul feeder flights). Perhaps allowing to manually change the XP earning per segment in a multi-segment journey?
7. Mileage earning rates based on the price is rather difficult as it depends on taxes and fees. Trick would be to find a reliable (and kept up-to-date) data source for airport taxes information. Perhaps that data can be crowdsourced too if the total dataset is large enough?

Anyway, very fun tool and project!